Are you seeing something like www.apple.com/support at the bottom of the screen? The idea is for you to contact Apple using that link. This site isn't that, it's just a user-to-user support site.
Having said that, you should not be having trouble setting up a Mac that has been properly prepared for sale. The first thing you should see upon turning it on is the "Hello" screen asking you to select a language. If you did not see that, then the Mac has not bee properly prepared for sale, and in all likelihood it will never be useful to you. In other words it's a brick, and you should return it for a full cash refund forthwith.
Read What to do before you sell, give away, trade in, or recycle your Mac - Apple Support. That is what a seller must do before selling it. Those steps are not optional.
Also, you may wish to review The All Too Common SAD Reality of Buying a Used iPad/iPhone - Apple Community. As its author states those principles apply equally to Macs. Briefly stated buying (or selling) a second-hand Mac is best left for very experienced Mac users.