What happens in a first session
What you will be asked, what you do not have to talk about yet, and what the 50 minutes are actually for.
A first session is mostly listening. You will be asked what brought you, what you have already tried, and what you would want to be different — but nothing is required of you that you are not ready to say.
It is normal to arrive without a clear account of the problem. Much of the early work is finding the words, and that is done together rather than expected in advance.
By the end you should have a sense of how the work would go and whether it feels like a fit. If it does not, you will be told so and pointed somewhere more suitable.