I want to contribute at ‘Jitsi’ so Could anybody please suggest me some thing so that I would able to solve some beginner level Issues on GitHub .
Welcome. Do you mean jitsi-meet or Jitsi Desktop?
There is no list of things available for fixing or for taking from beginners.
But a good start with jitsi-meet is to download the source, compile following the readme. You can than try running with webpack-dev-server, doing some source modifications and check whether you see them locally.
Okay I would try with jitsi-meet.