I assume you've watched one working, so my description will make sense. If I was more computer literate I'd attach illustrations from the manuals. I drove RJ
100s but I believe the system is identical to the 146.
Starting from the down position. The switch is on the cabin attendant's panel near the forward jumpseat. Hydraulic pressure (early RJ
100s required the cabin crew to shout "Power for the stairs please", upon which we switched on the AC
hydraulic pump. Later aircraft had an Airstair Accumulator, similar to a brake accumulator, so there was enough stored pressure to raise the steps a couple of times) from the yellow system goes to an actuator visible at the top of the stair, which lifts it clear of the ground. As it rises it folds in half so that on reaching the vertical position it is completely folded. It continues slightly over-centre into the door aperture and the cabin attendant's switch is then released.
The whole assembly is mounted on a cradle which slides aft on two recessed rails in the floor, into a recess just aft of the door, and is then safety-strapped in.
To extend the stairs, they are unstrapped, slid forward and pushed over-centre out of the doorway. The switch insn't used, as they self lower to the ground. If there was a Yellow hydraulic system problem they might not be damped, so would have to be lowered by staff standing outside. But we never did this in 5 years, being a bit dangerous.
Rear airstairs were an optional extra, the only ones I ever saw were those of Buzz. I believe they retract then slide forward into their stowage, as there's a toilet behind the door.
Regards - Musang