Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Sprite submissions for the current CAP closed a short while ago but come the next project you will be able to submit a sprite in the Sprite Submissions thread, as long as you follow the artwork that has been chosen from the Art Poll.
Welcome to CAP. You should probably start with reading the newcomers guide, found here. It contains a good part of information about what the CAP project details. The mission guide can also give you a good insight in what the goal of the CAP project is, which can be found here.