People who want to help bees often buy those little bamboo-tube bee hotels. They can help some species. But most of our native bees don't nest in tubes at all. They nest in the ground.
About 70% of North America's native bees are solitary ground nesters. A female digs a narrow tunnel into bare soil, builds a few chambers, stocks each with pollen, lays an egg, and seals it up. Her young spend most of the year underground before emerging as the next generation. These bees are gentle. They have no hive to defend and rarely sting.
What they need is surprisingly simple: bare, sunny dirt.
You can build what's called a bee bank in an afternoon. Pick a sunny, well-drained spot, ideally on a south-facing slope. Clear away plants and mulch so the soil is exposed. If your soil is heavy clay, mound up some sandy soil instead. Then leave it alone. No mulch, no tilling, no foot traffic. Ground-nesting bees can't use soil they can't reach.
That's the whole project. The hard part is doing less, not more.
Look closely and you may eventually spot tiny holes in the soil, sometimes ringed by little volcanoes of excavated dirt. That's a bee that moved in, raising next year's pollinators in a patch of ground you left open on purpose.