Talk about what brought you to the counseling center in the first place. Tell the group members what is bothering you. If you need support, let the group know. If you think you need confrontation, let them know this also. It is important to tell people what you expect of them.
Unexpressed feelings are a major reason why people experience difficulties.
The appropriate disclosures will be those that relate directly to your present difficulty. How much you talk about yourself depends upon what you are comfortable with. If you have any questions about what might or might not be helpful, you can always ask the group. I will be forced to tell all of my deepest thoughts, feelings and secrets to the group. You control what, how much, and when you share with the group.