laying cermanic tile

I have 3/4 plywood over 16 inch center studs. Do I need backer board, do you need to tape it (why) and do you put this set over the plywood and then lay the backer board

3/4" plywood subfloor on 16" O. C. Joists is good, that is the standard way. You didn't say what size these joists are and you didn't mention how far they span. Also see if you can read the species and grade too.

Yes you need another layer of either a cement backer or a membrane such as Ditra. Both are install using thin set mortar. Tape the backer? Yes of course.

Obviously someone told you how to do it but you have doubts. Please reply with the info I need to make sure your joists are stiff enough for tiles.

Jaz