When working on Upwork, please make sure that you have a contract with a client before doing any work, and ensuring that they have a verified billing method so that the work you do can be covered by Upwork Payment Protection is also a good idea. I'd suggest browsing this thread which has helpful tips for new users and you can also check out this thread for tips on avoiding suspicious jobs and scams if you haven't already.
re: "After performing work, how do I get paid?"
Without a contract in place, you can't get paid.
re: "Must he officialy 'accept' my proposal on the platform?"
To see if you have a contract in place, look here:
Upwork -> MY JOBS -> My Jobs
The client must click a green "Hire" button. That notifies you that an offer has been made. You must then click a green "Accept" button in order to enter into a contract. Talking on the phone and agreeing to something doesn't count.
Greg - How do you get paid.
And MOST important, yoiu learn how to use this site correctly before submitting any more proposals. Lick on the ? (question mark ) on the home page and choose Help and support. Then go through every section and link.