RAG ststus indicators

Enterprise Project Types – supporting a Project Management process that consists of 5 gateways à G1 – G5 – with a Schedule RAG status) can you please tell  me what is gate ways (As per my understanding they are phases) and how to create RAG status for the phases?

 one of these PDPs should be called  “Update PDP” that includes the capture of 2 subjective status RAGs that calculate a third overall RAG – calculation is your choice.  Can you please tell me how to do it? 

Thanks

Chaitanya

Geeth