You now simply click the big green "Use this template" button to use a copy of this repository as the basis of your own new repository under your github username/organisation (this 'template' status avoids complications with forks all being linked back to this repo).
Alternatively, if you aren't a github user, you can download a zip (see Releases button) and start your own repository with that.
Then see the User Projects guide page on the Chaste wiki for more information.