If you are hired through Upwork, then you receive money from Upwork.
Clients pay money to Upwork.
Upwork takes out a 10% fee to cover their service.
Upwork pays you the rest.
It's really quite simple.
If you want to actually use the money, you can set up a funds withdrawal method, such as withdrawing your money directly to your bank account (which is free in the U.S.!) or sending your money to your PayPal account. But that's really a different question.
You should never discuss "payment methods" with clients. If a client is trying to pay you via PayPal or by check or by some other method, then he is scamming you and/or cheating Upwork, and that kind of think will get you both kicked off the platform.