Upwork and Fiverr are just websites where businesses hire specialists for projects. You list what you do; they find you and pay through the site. That's the whole machine.
"Need help reviewing foreclosure files." A real company, a real task, a budget attached.
You send a short, friendly note: here's why I'm a great fit. A few sentences — not a cover-letter ordeal.
You agree on the work, do it, and the platform releases your payment. Safe and simple.
Most beginners start on one platform, get comfortable, then add the second. You don't have to do both at once.