The Ratings Preparation Course (formally Royal Naval Acquaints Course) lasts from Monday to Thursday and gives an insight into what you can expect at Raleigh, your chosen branch and the Navy in general. Normally people who have applied and are waiting for a date for Raleigh go on one of these.
The Look At Life Course is shorter, running Tuesday to Thursday and gives a general overview at life in the Navy. This is normally aimed at schools/colleges/ people who may be thinking about joining up but haven't signed up yet
And any course with (SM) is for people going / thinking about going submariner