The problem many people have with Saga grapple is that you can't do anything without taking feats for it. But in essence:
Grapple checks are still in. Stupid size bonuses are still in but now follow the universal -10 -5 -3 -2 -1 0 +1 +2 +3 +5 +10 progression.
Make an unarmed attack vs reflex defense to grab, if you win make opposed grapple checks.
Attacker (if they win) can choose to trip (need Trip Feat, if you win opponent's prone, grapple over) or pin (need Pin Feat opponent takes no actions next round).
If tripping you can also throw with the Throw feat to move them into another square as well, if Pining you can deal damage with the Crush feat.