How can I toggle gravity for a single rigidbody?

How do I make it to where,the player right clicks on a rigid-body and disables/enables gravity for that one object?

You should look at this as two separate problems:

  1. How do I affect a game object by clicking on it?
  2. how do I turn gravity off for a game object?

Take a look through the documentation and please remember to use the search function on this site. There are answers to the individual questions; you just have to look for them.