Here are some GitHub useful command in daily development life.
Open the command line / Terminal / GitBash
Navigate to the directory where you want to use the git.
CD /var/www/html/github_demo
1. To make you current directly managed by the Git program
$ git init
2. Now add all the files to the git in initial commit, run
$ git add .
3. Create your first initial commit, run
$ git commit -m "inital commit - project files"
4. Now add Git Origin, the below highlighted URL should be your github repo URL:
$ git remote add origin https://github.com/your_username/Demo.git
4. Now push it to the GitHub
$ git push -u origin master
Now check your GitHub account for the latest changes.