whether to use gh-pages or master branch

So i was trying to use github pages feature. In a youtube tutorial the guy said that we need to commit only on the gh-pages branch. My question is : whether to use gh-pages or master branch? 

usually the master is used to develop the code, while gh-pages only serves for the github pages feature. It is not a rule it is only to have a distinction between development and documentation. You can put everything in the same branch, but more you’ll develop in the repository the more confusion you’ll have with just one branch.

-Gabriele-