To clone the repository, you can click on the clone or download button which gives you the link to the repository. If you would prefer going through the command line or Git Bash, you can use the following commands.
Change directory to the desired location you'd like to clone the repo into. i.e cd folder-name
git clone repository url.git
Don't forget to add the .git at the end of the repo url
Cloning the repository downloads the files into your desired location and local git
Edit and contribute as you desire.
Add and commit the repository on your local git before pushing to the remote git.