There are many configurations. Some have blocks, rollers, or if it's like mine, just a plastic curb that spans the length of the slide and is built into the floor at the very outside edge. As the slide comes in the entire underside simply rubs against this piece. It should cause the inside edge of the slide to tip up and not rub too hard on the carpet if all is working well.
My slide started to rub on the carpet much harder than when new. A careful inspection revealed the plastic curb had cracked in the middle - probably from me stepping on the raised floor of the slide when it was only partially out.
I modified mine by adding 2" X 10" metal conveyor rollers (capacity 1200# each) that are recessed into the floor. The outside 10" on each side of the slide rolls on them and it works silky smooth. I adjusted the height of the rollers to keep the slide from smashing and rubbing the carpet.
