how to set a github repo to automatically pull from upstream code example

Example 1: how to update local repo when i make changes to github remote repo

git pull origin master_or_other_branch_name

Example 2: fetching a forked branch

$ git remote add theirusername [email protected]:theirusername/reponame.git
$ git fetch theirusername
$ git checkout -b mynamefortheirbranch theirusername/theirbranch