where do I put in the transmission fluid?

Well if its a slow leak you can just pour it down the automatic trans dipstick tube, that is the easiest way (not sure where it is on the Jimmy, but if you see another dipstick other than the one attached to the front of your engine, that's it). If it is pissing out (missing drain plug or case impact damage) just have it towed or you will run the risk of causing irreversible damage that will warrant a replacement or rebuild. Good luck.

Where is the dipstick located

How do you get the transmission filler tube out of a 1996 GMC Jimmy?