I tried git push on master branch but it just shows that I have new pull request but when I click on new pull request it takes me to comparing changes but doesn\'t show any
The main branch has already replaced all new github repos as the main branch. You can read up on it here. There is no actual difference between main and master, it's just the name of the default branch.
For you git push origin master just creates a new branch called master (since it doesn't exist already) and pushes your current commits there.