I am not able to use pull, push, branch merge

Question

I am not able to use these below commands

pull, push, branch merge 

$ git push origin master
To https://github.com/jnan2017/firsttest.git
! [rejected] master -> master (fetch first)
error: failed to push some refs to "https://github.com/jnan2017/firsttest.git"
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., "git pull ...") before pushing again.
hint: See the "Note about fast-forwards" in "git push --help" for details.

Answer 1

Please execute the below command in the terminal to solve the problem:

1. git pull origin master --allow-unrelated-histories
2. git pull origin master
3. git push -u origin master