buying from "for sale by owner"

I am looking at a four-plex and its for sale by owner. They don't want to use a real estate agent to save some money.

If I don't have a real estate agent, how do I make an official offer? How do I get it under contract?  I didnt see any documents in the tools section.

If I do have a real estate agent do I have to pay him out of pocket since (I believe) that his commission wouldn't be paid for by the sellers.

Thanks.

Shane