If I bought a iPhone from someone can they keep track of anything I’m doin on tit

Make sure they did the things in this document --> What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

You can do some of them yourself but if the person did not disable the Find My feature then you have problems down the road.

Not unless they didn't sign out of their account and you didn't set up the phone from the "hello" screen.