You can start modding by just creating random stuff, whatever your mind can think. I highly recommend just starting with simple weapons and then working your way up from there. Have you looked at the tutorials lying in the General Mod Discussion? They might help you get to more of the advanced stuff on tAPI modding. Also, if you have any problems, just look through other people's source code by using an archiver like 7zip and WinRar and opening the .tapi file, since tAPI files are basically zip files... After that, just post it up on Works in Progress, maybe if you feel you are done, to Released.