Oksana Dudyk scanned a small selection of ornamental plants lining the shelves of her new florist shop, recently opened in this city on Ukraine’s western frontier. Her eye landed on the perfect bloom for a new customer: fuchsia-colored primroses, vivid and lush, ideal for brightening an austere corner.

It was late afternoon, and the flowers were only her 10th sale of the day. But that was nothing short of a miracle for Ms. Dudyk, who started the shop with her last savings after fleeing her now-decimated hometown Mariupol under a hail of Russian rockets. Her husband, who enlisted in the Ukrainian army after the invasion, was captured by Russian forces in May and has not been heard from since.

“These flowers help me to get by,” said Ms. Dudyk, 55. A former construction engineer who before the war helped design and build schools, she said that she never imagined that she would one day sell flowers to survive. “They bring me joy, and they help customers too, by creating a positive atmosphere in this incomprehensible war.”

Ms. Dudyk is among thousands of Ukrainians who are picking up shattered lives and trying to start over, many creating small businesses that they hope will bring them and their new communities fresh purpose. Others are working jobs that are a step down from positions lost because of war, grasping lifelines to keep their families afloat.

“The Russian invasion has spurred a lot of people to pull up and start building new businesses,” said Andriy Sadovyi, the mayor of Lviv, which has become a locus for people fleeing the war-torn east. The government is encouraging this entrepreneurship by offering grants, zero-interest loans and other financial support for small businesses.

“Ukraine will remain unbroken,” he said, and a big part of that involves “ensuring that the economy develops and thrives.”

That would seem a daunting prospect as Russia prepares for new attacks in Ukraine’s east and south. Ukraine’s economy is projected to shrink by a third this year, according to the International Monetary Fund, and an estimated one-fifth of the nation’s small and medium-sized businesses have shuttered.

But many refugees who have fled war-torn areas are collectively forging a new front of economic resistance to Russia’s aggression.

The foundations are being laid by people like Serhii Stoian, 31, a former math professor who opened a tiny storefront selling coffee and fresh pastries in Lviv after fleeing a job in Bucha, the city now infamous for scenes of unarmed civilians killed by Russian soldiers. The cafe, named Kiit, after his cat who is missing in the war, struggled in its early days. But business is now so brisk that he is opening a second one in Lviv. A third is being planned for Kyiv.

“We came here with $500 in our pockets,” said Mr. Stoian, who now employs four people and works with a friend who became a business partner. “When we started, we promised to pay the landlord back in two months. We were able to pay him in just two weeks.”

Mr. Stoian had dreamed of opening his own cafe but never did, fearful of failure. As a side gig to teaching, he operated a YouTube cooking channel in Ukraine called Hungry Guy Recipes that has nearly 700,000 followers. “Life was pretty great,” he said.

He had just begun a part-time job at a bakery in Bucha, making pastries from his YouTube recipes, when the invasion brought everything to a halt.

“The bakery owner called at 5 a.m. and said, ‘We are being bombed. You have 10 minutes to join me if you want to escape,’ ” Mr. Stoian recalled. “My friend and I didn’t have time to think, because when you hear that Russia is invading, you can’t think,” he said. “I was worried about my cat, who was staying with neighbors. But we grabbed some clothes and documents and jumped into the car. And we drove like crazy.”

They wound up in Lviv, where they lived in a shelter jammed with other refugees from around the country. For three weeks, they helped women and children cross the border. But they needed paying jobs.

When Mr. Stoian saw a “for rent” sign on a tiny former souvenir shop, a light bulb went off. “We could rent that and sell coffee and pastry,” he recalled thinking. “We had no business experience. And we were a little worried because there is corruption in Ukraine. But my friend knew how to make coffee. And I could bake.”

They rented an espresso machine, and Mr. Stoian stayed up nights making fruit pies, rosemary cookies and cinnamon buns. But no customers came. Mr. Stoian began to despair. Then he erased the menu from the cafe’s chalkboard facing the sidewalk, and began to write out his dramatic tale.

“We moved here because of the war,” the message said. “We want to do what we do best: Make great coffee and pies. We believe in Ukraine. People have helped us and we want to help others.” He pledged to donate part of the shop’s proceeds toward the war effort. Military personnel were offered free coffee.

The next day, he said, there were lines of 20 to 30 people. After posting on Instagram, the cafe had up to 200 customers a day. It has been such a sensation that he has received inquiries about opening Kiit franchises.

Though buoyed by the success, he still grapples with the pain of the senseless killings of people he knew in Bucha, and the loss of his beloved cat, who his neighbors left behind as they fled from shelling. “Naming the cafe after Kiit helps me to go on,” he said.

On a recent day, he swept his eyes over the bare walls of his second Kiit cafe, the floor cluttered with construction equipment. “This is all still a gamble,” Mr. Stoian said. “And if we lose everything, that would be OK, because we started with nothing,” he said.

“But maybe we will also make it. Maybe we will be the next big success.”

For others, resilience means accepting a more awkward transition. Kirill Chaolin, 29, worked as a high-ranking trainer for air traffic controllers at Lviv’s international airport. His job was wiped out when Ukraine shut its airspace to commercial flights. In the last few months, Mr. Chaolin, who has a wife and 5-year-old daughter, has begun driving a taxi for Bolt, a rival to Uber, to get by.

“It’s hard to step down from a big job to do this,” he said, navigating through a crunch of traffic on a recent weekday. “But there is no choice: My family needs to eat.”

Scores of his former colleagues at Ukraine’s airports are doing the same, he added. “You must do whatever you need to survive.”

People like Ms. Dudyk are remaking their lives even as they struggle to surmount the war’s heavy toll.

She and her husband had been living a tranquil life in Mariupol, the port city that was one of Russia’s first strategic targets, and were about to visit Prague for vacation when the invasion started.

“We had decent salaries. A happy home,” said Ms. Dudyk, who has two children and four grandchildren. Her husband ran a window-making business and worked on the side as a beekeeper, tending 40 hives. As a construction engineer involved in significant building projects, Ms. Dudyk had a job that made her proud.

When Russia attacked, she and her father, aged 77, tried to hold out until a powerful blast ripped off the front of her house while they were sheltering inside, forcing them to flee under continued shelling toward Ukrainian-controlled territory.

Ms. Dudyk said her husband, 59, enlisted to fight the day Russia moved in, and joined Ukrainian forces inside the Azovstal steel factory. He was among 2,500 fighters taken by Russia as prisoners of war in May, and she has not heard from him since. Last month a blast at the prison camp left more than 50 dead, but Ms. Dudyk dreams that he will one day come home.

Today, home is a cramped shelter in a temporary modular town set up for Ukrainian refugees, where she lives with her father.

“I want to make the flower shop a success,” said Ms. Dudyk, who is expanding it with guidance from another refugee who once ran a nursery. If all goes well, her spartan storefront will be transformed with new shelves and more flowers.

Most of all, she wants to sell roses: “My husband always would bring me big bouquets,” she said with a smile. “But for roses, you need a refrigerator. And I don’t have the money.”

With her savings low, Ms. Dudyk has applied for a grant under the government’s program to support small and medium-sized businesses.

She takes nothing for granted. “When your country is being bombed, you realize that your life is threatened and everything can be taken away,” Ms. Dudyk said, a sunny woman whose blue eyes cloud with tears when the painful memories surface.

“You are planning for the future one moment, and in the next you lose everything. You start fighting for bare necessities — water, the ability to make a phone call to tell someone you’re still alive,” she said. “You wait for the nightmare to end, then you realize that the invasion is of such a huge scale, so what is the chance?”

As she spoke, a stream of customers filed in, and her face brightened. A deaf couple approached and gave her a hug, making the sign language symbol for tears — and then, a heart. She showed them her latest floral lineup, and they pulled out their wallets.

“I’m not a plant expert, but I know what can cheer people,” said Ms. Dudyk, who said she derives strength from a remarkable show of solidarity and support from her new Lviv neighbors. “Thanks to them,” she said, “I know I am going to make it.”