That is great that you want to contribute! I wish I understood code so I could contribute too but I think I am too old to learn it now Take a look at the developer documentation here http://docs.moodle.org/dev/Main_Page and in particular this http://docs.moodle.org/dev/Plugins and this http://docs.moodle.org/dev/Guidelines_for_contributed_code
General developer forum
How to get started?
Please Mary, no. Neither of us are too old, nor are we too dumb, but we have far too little time to spend learning it. We are teachers with all the responsibilities that implies, parents with grown up children, you are the fabulous MoodleFairy, whereas I am just a Moodle lightweight. So please...