You can find your websites FTP details in the Website Dashboard for your site. To find these, first go to the Server Dashboard and click the Cog icon to go to the sites Website Dashboard.
From the Website Dashboard, Click on FTPS SSH & Git in the left hand nav bar
At the top of the FTPS, SSH & Git page you'll be shown your sites FTP credentials. You'll need three pieces of information to connect via FTP which are the servers hostname, the username and password which are all indicated below:
For a quick and easy way to connect using FileZilla, you can also click the download icon shown to the right of the details to download the FileZilla config file.
If you need an FTP client some popular programs for Windows are FileZilla and FireFTP. CyberDuck, FileZilla and Transmit are popular for Mac.