Mostly they just ask a question and let you talk, cry and just generally get it all out in the open. I've only ever seen one and I found it hugely helpful, hadn't felt able to cry because I was holding things together for everyone else's benefit and just having an hour where it was fine to just fall apart, did help.
I would definitely echo that. Was amazing to have someone who I was totally comfortable was not going to judge me, no matter what I said. It was just a time to be able to say anything I needed to or wanted to, and to cry.
I have to add though, that I know other people who have had rubbish counsellors. Don't be afraid to ask to change if you don't feel comfortable with this one.
I'm back on the waiting list for counselling because the first one I had was a bit of a tool but even so, the three sessions I had with him were variously useful. It was good to have a whole hour to talk about ME . I did find it painful though, the couple of days after were always very chaotic emotionally, so be prepared for that if you go for it.