I have been in a lot of groups and have been screened quite a bit. Usually they want to see if you are going to be a good fit, get along with the other members, not attack them or have unresolved anger that you are going to unleash upon them. Also they want to make sure that you are not going to be overwhelmed by what is going to be discussed to the point of being suicidal or self harming. They will probably give you some idea of what the group is about and how it is run and a low down of the rules.