The entrance interview basically means that they explain to you everything you have to go through - i.e. medical examination, basic training, oath, etc. First you have to sign a few documents and go through a full-day medical examination. Basically, it seems like you have to commit to the fact that you want to be there and you are not very sure that you will do the position you want. I don't know if that's true, but it seems that way.
