Adding features to mission planner

I want to add features to mission planner with programming. for example I want to have a tab of air drop in my data. what skills do I need to know? (I know you need to know C# but what else?)

also I wish to know how to navigate and understand the code. because to me it looks really messy
and I have not found any documentation on the code structure.

cheers and thanks.

thank you, seems very informative.