When the slide is racked all the way back manually or by reaction to a shot, the farthest sear in the back, which is fixed in the frame, catches the striker and keeps the striker there, compressed and ready to go, until the trigger is pulled. The trigger mechanism moves down the sear letting the striker go forward (SA).
If the striker doesn’t detonate the primer, it stays in its relaxed position.
When the trigger is pulled again, the second sear, which is way forward, moves back, catching the striker and moves it back compressing the spring. At the end of its travel, this second sear moves down releasing the striker (DA).
There are two other pistols that I know use this same mechanism, the Walther P99 and the Canik TP V2. These last two have a button in their slides that pushes the SA sear down, fulfilling the function as a decocker.