A git repository can be cloned from the apps tab.
Once cloned you will be provided with a SSH key and webhook url.
These can be used for automatic deployments for whenever you push to the master branch.
If you are using bitbucket you can add your ssh key in:
Settings -> SSH Keys -> Add key
And you can set the webhook url in the repository Settings Webhooks -> Add Webhook:
Then you're done!
Any changes you make to the master branch of the repository will be reflected on the website within a minute or so of pushing them.