Run it out until it "clicks" (or rips, or burps, whatever) and then release the switch.
There's a little clutch in there that knows when to quit pushing out. That's the noise you hear, like on a good electric screwdriver with a variable torque setting. Same thing.
On the first few trips check to make sure all the seals are good and tight. If they do it right the first few times then don't worry about them anymore.
Same bringing it in.
BTW: I leave the exit door open when moving the slide room. You'd be surprised how much air is displaced. Makes the motors job easier. And airs out the trailer!