Transmission

I bought a 1991 ford f150 drove it almost 100 miles and on the last ten miles it overheated. I came back the next day to pick it up and it started and ran great when i put it in drive it seemed to shift but would not actually drive. i looked underneath and there was transmission fluid everywhere. i am looking to replace all my lines there is no obvious breaks. Do i need to replace the whole transmission? its completely drained of fluid. I have not had a lot of experience with cars just minor tune ups and what not and would like to use this as a learning opportunity but i am a little overwhelmed and dont have much of an idea where to start.any advice would be greatly appreciated! thanks in advance.

I haven't been driving the poor ole girl wont even move unfortunately, which sounds like that may be a good thing. i really appreciate the advice tomorrow i will trace the lines and see if i can find a leak. what would be your advice on fixing the leak? just replace that line or is there some way to patch it?

Transmission End so you would suggest new seals? I would assume it needs them anyway even if its not the issue.