for strip sets AKA drop sets you start with a weight you can do for usually a relatively low number of reps and when you're stuck you pull some weight and do a couple few more more. You can drop as many time s as you can stand, but after 2 or 3 at the most you've gotten what you will out of the set.
Example: snag some extra pins from machines nobody is using. For pulldowns lets say. Put a pin in the stack for a weight you can do 6 reps with, one maybe 3 plates up and one more 3 or so up from there. When you're stuck on the 6th rep yank the bottom pin and do a few more until you're stuck again, yank the next pin, a few more. You'll know when you're done.
BTW, this is useless and maybe even dangerous with some movements if you don't keep the form tight and in any case it will kick your ass, especially on big exercises. Get a couple buddies to pull some plates off the bar on each side for some full squats in the rack like this and being injured in a violent auto accident may seem like a relief by comparison.