If you are serious about pitching a TV show, you are first going to need an agent. They have ways of getting you meetings with potential television corporations.
The next thing, is the actual script for the pilot show. You could have other episodes, but it is essential that you have the first episode. A production company is going to want to see this.
Finally, you are going to need a treatment/summary of each episode for the entire first season. If a company is to invest in a television show, it has to have legs. They want to know that the suspense will carry over the entire season.
Having in hand a short summary of the events that would happen in the second and third season could also help.
Remember, you have to have a story for the ENTIRE SERIES, not just the pilot or first few episodes.
Good Luck.