Ask HN: How to begin contributing to an open source project?

I'm a fourth year college student with a few years of programming classes, but not much outside-class experience. Many people have said that contributing to open-source projects is a good way to show off your ability level and to learn more about how to code. I'm not sure how to begin - in other words I don't know what I don't know about open source projects.

Which open source project should I contribute to? How do I know what part of the project to work on? How do I get the code and how do I submit changes? How do I ask for guidance/get feedback, besides asking HN? Which IDE should I use?

Thanks for the advice, Kevin