Where a beginner can start contributing on Open Source projects? Github? Or there's something else?
First off stick with projects that you're passionate about, or at least use regularly.
- Get involved in the open, ongoing and public discussions about the project. Help other users of the project, and generally talk about the project when ever you can.
- When you have something to say, raise polite bugs, issue of other suggestions.
- It you can create patches or merge request for these things.
- User the tools (github, sf, etc...) and contribution guidelines outlined by the project.
- Don't be discouraged if these efforts don't get accepted or receive much traction. It's possible the project owner is trying to move in some other direction.
If your at this point, your already a contributor, and I'd argue a senior member of the project. Good luck.
- Once you have some confidence, you can submit patches/ merge requests for current bugs, or even your own feature requests.