First off, welcome to the open source community! To start contributing, I would suggest that you find a project that seems useful to you and which you can use on a daily basis. Good projects usually have a 'CONTRIBUTING' document you can read and figure out how to start contributing. A contribution can be as simple as correcting a typo or as complex as finding a bug that would crash the entire system in certain conditions! It can seem intimidating at first but maintainers are usually swell guys/gals. When in doubt, just shoot them an e-mail. Good Luck!