They do a lot! But it's not part of where the money comes from.

Imagine a normal grocery store. Then imagine it suddenly gets a button that makes more stock magically appear on the loading docks. Almost as much as they've sold since the last button press. It's great for profit margins, but the employees still have to do their jobs, and their jobs are basically unrelated to the magic button.

Most of them are sales people. The OP is correct, banks increase the monetary supply through fractional reserve.

Yup, thin air. When people borrow money, the bank just creates the money out of nowhere. That money doesn't actually exist until the debt is paid. Banks are ultimately responsible for the extreme inflation of virtually all currencies currently in use.