Thank you for pointing this out. As I'm new to this stuff , I don't know anything about this.

I want to take backup of sql server data to another drive and online backup also.

Yes. and I am not able to understand above paragraph from the documentation. Can you please help me with this?

dba.stackexchange.com/questions/193076/… In this article, It's written then when one of the server crashes, qourum doesn't have time to transfer vote so can I recreate that scenario.

I have already gone through the docs but still I'm confused. Whenever I'm shutting down one of the nodes, cluster isn't failing.The other node which is running is simply gets a vote and I'm able to force-manual failover of the database of AG from the one I shutdown(which has primary database) to the other which is running(my secondary database).I don't see any reason to use witness.