Hi Sanjeeb

The best way to work on and contribute to projects is through projects at your university. Ask your professors in relevant fields, they will most certainly have ongoing projects that you can be a part of. That being said, some important topics that you could work on your own are:

• Building web applications
• Building GUI framework
• URL shortener
• Digital post it notes etc.

The implementation for all these can be found easily on github.

Hope this helps!