SHELL

Updates were rejected because the remote contains work that you do

git pull origin master
git push -u origin master

Updates were rejected because the remote contains work that you do not have locally

git remote add origin [//your github url]

//pull those changes
git pull origin master 

// or optionally, 'git pull origin master --allow-unrelated-histories' if you have initialized repo in github and also committed locally
//now, push your work to your new repo

git push origin master