Can someone explain how a uncircumcised dick works?

Hi. So this might sound really childish, and I’m sorry but I’m 17 and I gave my first handjob last night. It was to my boyfriend who is uncircumcised, which never bothered me but I’ve seriously never been so confused. Am I supposed to pull back the skin? Or just do it with the skin? I’m sorry if this is a dumb question, just really confused lol. Thank you.