Discuss a personal value that you are proud of and an experience that helped or led to it's development. They will send you the paper to do that on, and your application, drug use certificate, medical exam information, ect. All that information will be in the booklet, also. You'll sit in a room with other cadets who are waiting to be interviewed. Then you will go, sit down, be interviewed, and leave.
Length depends on how many people are there, business, ect.