Which ones fit on my mustang? Also what is the difference between an exhaust and muffler tip?
To answer your questions
As long as the ID (inside diameter) of the tailpipe is the same as or a touch larger than the OD(outside diameter) of your exhaust it would fit. Assuming you want a bolt on and not a weld on. If you want it welded you can either get one to slip over your exhaust pipe and be larger, or get the same size and butt it up to weld. Either way.
That being said typically exhaust tips on our cars are around 18" long. Our SN95 bumpers dont have cut outs for the exhaust because they dont reach low enough, thus leaving all of the exhaust from the tire back visible. So the longer exhaust tips are visible and look at home on our cars, vs a stubby, short exhaust tip you may find on a s197 or new mustang, as the only thing visible on those cars is the last inch of the exhaust tip so length doesnt matter.
To accurately tell you what exhaust tip would work we would need to know if you have a stock cat back or aftermarket. And how long your current exhaust tips are.. if they're already the stubby short style, you can replace them with the same or cut more of your catback out and install a longer one. If they're currently long, youd need to replace them with a new equally as long one.
To answer your question exhaust vs muffler tip-
A muffler tip is an exhaust tip that generally mounts right to the muffler. These are found in, for example, a s197 where the muffler is right behind the rear bumper, and then a short tip is attached to that to exit the bumper, which is why muffler tips are pretty much universally short. Our cars have mufflers before the axles, so if you put a tip on your muffler it would not be visable... however theres nothing stopping you from installing a "muffler tip" to any part of your exhaust, it does not HAVE to be attached to the muffler directly.
When you say "exhaust" in exhaust vs muffler tip, if you meant just exhaust, exhaust is a broad term, but broken down basically you have exhaust headers/manifolds, exhaust mid pipe (H or X), exhaust axle back(contains the mufflers and over axle piping and sometimes the exhaust tips too) and then exhaust tips, so exhaust isnt the same as muffler tip, but if you meant exhaust tip, it's basically the same as muffler tip, but things advertised as exhaust tips are probably going to be longer than a muffler tip, and would be more of what you probably need.