Were you hurt?
If yes, they'll pay any medical bills and offer a settlement (the amount varies depending on the extent of injuries).
At that point, sign nothing, say nothing, and get a lawyer.
If you werent hurt, its standard proceedure for an insurance agent to want you to sign whats called a "waiver of liability" to protect them from you from coming back months later and saying that suddenly something hurts.
They will usually make an offer of a few hundred dollars to get you to sign that waiver, saying something along the line of "to cover any incidental expenses you might have suffered".
That waiver is the most important piece of paper to them, as paying for future medical expenses can cost them a fortune.
If you arent hurt, do not volunteer that you feel okay.
Just say something like you're feeling a little sore after the accident.
That puts the other guy's insurance agent on guard, and at that point he'll offer some extra money to get that waiver signed.
Just remember he wants that waiver of liability signed, and he wont hesitate to make it worth your time.