I had someone offer to mine bitcoin for me, I am a beginner
Sadly there are a lot of scammers around. Don't pay to anyone you don't know (and before you sign up on an exchange, make sure it's a reputable one).

There are also some services which allow you to buy "a miner" which mines for you, but generally, you would be better off just directly buying whatever coin you want yourself.

Be careful, don't trust strangers.