Tips please!

I have made an appointment with the mental health specialist at my doctors surgery and was surprised that they could see me on Friday.

Its taken me years to make that call and I thought I would have a week or so to figure out what to say so now I'm freaking out!

I think I have social anxiety or social interactions are where most of my problems lie. But does anyone have any tips for the first time speaking to a doctor hoping to get some help preferably therapy? I'm just not sure whats best to talk and about or mention. Like how do I start when they first ask me why I'm there?