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!

I started long time ago (before Sourceforge became a big thing) by using 'free' software; free is an in free speech. Note: Sourceforge was the king before Github.

I reported errors such as installation issues, translation issues, app crashes or other abnormal or unexpected results and behaviors. Then I started to provide translations or fix typos (even though my English is bad) because the next guy may update/fix my stuff too - still better than nothing. Or simply asked for new features or changing features; giving feedback.

The whole process was terrible back at that time. Mailing changed files, trying to ensure the repository owner has still the same file version which my work based on - so he may replace his file by mine easily. Carefully trying not to put too many guys on CC but still have enough devs addressed to get my changes 'merged'.

Sourceforge was a paradise when it became popular but since Github, it's even easier. Now you can contribute to virtually any project by doing almost 'anything'. Asking question to a particular project, writing a short blog post about a newly gem you've found or tweeting about a problem you can't figure out by yourself. All of this is already relevant to open source projects.

Contributing to projects by adding, changing, or deleting code is maybe the next step. Look for existing and yet still unresolved issues. Try to fix them and provide some evidence about the fixes like adding test cases. Or implement new features.

If Github is a myth ATM, well they have good documentations help.github.com/desktop/guides/contributing If Git is a myth ATM, well they have good documents too https://git-scm.com/book/en/v2

Be involved :-)

Don't sweat it, if you feel so intimidated, create an anonymous github account and just do it (granted you are actually trying to contribute). Check here for some guidelines: github.com/blog/1184-contributing-guidelines

I started when I stumbled over the Atom editor project, about what... 2 years ago? This was just before they first open-sourced it (Electron was still a neat little sub-project of Atom called "atom-shell").

I loved the idea of using web tech (since I had just started learning Javascript) and how vibrant and cooperative the budding community was at the time. So I started engaging on their forum, and familiarizing myself with Github. I helped with issue triage, solving newbie problems etc. Eventually, I also contributed to Pull Requests and opened one or two of my own, which was amazing:

It taught me about best practices on Open Sources projects, Git and Github-based development workflows, how to cooperate with people across the globe etc.

As I'm not a full-time professional developer, the community eventually grew over my head when I couldn't spend much time there anymore. But Atom is still my editor for everything and I have a lot of love for it mostly because of the Open Source experience it gave me.