You need to read the Driver doc page. It's all there.
1) Configure all devices on the caseta bridge first. Add and name all of them;
2) Enable Integration or Telnet Support on the Advanced settings (or something like that);
3) Add the RA2 Select Bridge driver and configure it's IP;
4) Add the devices to your project using either Caseta or RA2 Select drivers (Lighting, Switch, Fan etc). I would suggest only using RA2 Select drivers as they work the same;
5) Open the Caseta app and export the Integration Report (something like that). This will give you all the IDs
6) Go to Composer Pro and do the correct bindings.