How do you pitch a new program to the studio?

when pitching a new program, do you need an entire season (13 episodes or more) already planned out? Or is it only, characters and plot? Does one only need to pitch the Pilot episode? and when they accept it, thats the time they’ll do the rest of the episodes? How does one do this? Do they send it through mail? How to legalized it, so no one can copy it? Any information you can give will be helpful. Has anyone done this before or knows anyone, please share the experience. Thank you.