Questions from a beginner

Greetings folks, new guy here.
Having a little problem figuring out how to work Local Monerro.
Do I need to money in my digital wallet on LM, or can I pay the vendor directly through the Cash App?
While attempting to upload funds to the digital wallet on LM, it seemed to me that Cash App did not want to take the receive code.
I know if I send funds to an incorrect address, they will vanish into cyberspace never to be seen again, so I am a tad bit cautious.
I appreciate anyone that will take a few minutes to help a new guy out.i

You pay the vendor directly through CashApp if you mean paying in fiat.