Don't be afraid to edit! Just find something that can be improved and make it better. Other editors will help fix any mistakes you make.
It's normal to feel a little overwhelmed, but don't worry if you don't understand everything at first — it's fine to edit using common sense. If you have any questions, just ask a more experienced editor on their talk page or message board.
If an edit you make is reverted, don't edit-war over it, discuss it on the article's talk page
