I have just finished one job. I've sent it by message to my client.
My client wants to pay me but he doesn´t know how to do it. How does he do it ?
Do I need to click on "End contract" before getting paid ?
It looks like a fixed-price job. The fee should have been in escrow before you began work. If so, then click the green button to submit the work and get paid. That starts a 14-day clock during which the client can request changes and/or approve payment. If the client does nothing, you'll automatically be paid in 14 days. (And the money will be available to you five days after that.)
Before accepting another contract, you should read the information available at the links above, as well as other information about how this platform works.