Q: i bought an iphone 4s but it still has the old owners aplle id on it. How do i get pass it?

It sounds like your iPhone is Activation Locked, as described here.

Find My iPhone Activation Lock - Apple Support

You must contact the original owner and have that person remove the iPhone from Find My iPhone or the iPhone will remain useless to you (as described in the article).  Return it for a refund if you cannot contact the owner.