add a new branch to github

addnewbranchgithub.md

mnelson:myproject mnelson$ git push origin my-new-branch
Counting objects: 3, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 313 bytes | 0 bytes/s, done.
Total 3 (delta 0), reused 0 (delta 0)
To https://github.com/cubeton/mynewrepository.git
 * [new branch]      my-new-branch -> my-new-branch

Hi, I came here from https://product.hubspot.com/blog/git-and-github-tutorial-for-beginners

I'm sorry but I am rather confused. If you've made changes to a branch locally, why wouldn't you just push only your amended branch to github? Why push the master branch first? I don't understand. Or if your new branch is an amended version of someone else's master branch, wouldn't you need to clone their master to your local machine first, not create a brand new folder and push the master? Thank you if you can clarify.