It is recommended to use a new address every time - for privacy and for security. You can simply reuse the same receiving address but it is not best practice. Lots of people do it though.
Your Bitcoin Core wallet has already generated a pool of (100) addresses for you to use. Every time you hit "request payment" it shows you another one.
So if I post an address on a website and multiple people sent bitcoin to it I'll be OK? I'll get all the coin?
100 addresses? That's insane. That's like going to the bank and them giving you 100 checking account numbers. WTF? I thought it was safe to post and use an address?
Rather look at those 100 addresses like you've been given 100 individually coded cheques
