You go through an addmission process that's pretty much similar to an employement process (several interviews, technical interviews, tests etc).

After you get in, most of the jobs you get are strongly limited to your particular skill (so you won't be able to see what coding jobs are available if you're a designer).

Then, the customer aquisition process is slightly different, as you don't talk straight to the client while you're „bidding”, but with a recruiter, who deals with selecting the right candidate for a job.

Finally, for most of the jobs you don't even have to _apply_, as recruiters constantly send you messages for potential jobs.

Now, upwork & freelancer are mostly a race to the bottom; I personally got banned from upwork for having the audacity to apply to jobs and not winning any (because I didn't wanted to work for peanuts).