I have to agree that the Reese manual slider is a real pain in the butt; I believe I have figured the thing out finally, though.
First, lube the thing, per the manufacturers instructions. I find it is not generally necessary to drop the front legs, but it does help to take the strain off of the slide. Move the lever to maneuver, lock the trailer wheels and pull forward - gently - you will hear it click into place. CHECK THAT IT IS ACTUALLY LOCKED!!!. Pull the legs up and you are ready. Same process for tow mode.
Had I to do over, I would have possibly bought an auto slider model, but I hear they are heavier than a horse. My Reese is hard enough to get out of the bed so maybe that's the tradeoff. The Sidewinder with air looks like a really cool option, but I am OK with what I have for now.
DW also tends to have a kitten when I am moving the slide. Freaks her out!!