The first thing you need to do is go on to https://github.com/crowdresearch/crowdsource-platform, and click on fork.
A fork is basically a copy of a repository. Forking a repository allows you to freely experiment with changes without affecting the original project. Once you are sure of your changes, you can raise a pull request to the original project to merge your changes to the original project.
When you have forked the project, you will find it in your github account
Now, you want to get this forked repository onto your machine so you can start making changes to the code. Cloning refers to getting the code onto your machine. You can clone a repository by typing in
git clone https://github.com/<your-username-here>/crowdsource-platform