When you are contributing to an open source repository on GitHub, you are allowed to make pull request only through forked repository. In that case, you will always need to keep your fork updated/in-sync with origin/master. You can follow below approach through command line to do that:

1. Clone your fork from Origin
   

   git clone git@github.com:YOUR-USERNAME/YOUR-FORKED-REPO.git

2. Jump to the root directory of your cloned fork
   

   cd {cloned fork path} e.g. cd D:\cloned\fork-repo

3. Add remote from original repository in your forked repository
   

   git remote add upstream https://github.com/ORIGINAL-USERNAME/REPO-YOU-FORKED-FROM.git

   git fetch upstream

4. Updating your fork from original repository to keep up with their changes
   

   git pull upstream master