I think GP's are sort of like family doctors (I'm from the USA), and if so, I think in my experience my family doctor asked me some questions about my background (what school was like, how I'm feeling, how long I've been feeling this way, why I think I'm feeling this way, whether there's anything in particular that's bothering me, etc.). He took notes of what I said. Then, he referred me to a counseling center's psychologist by directly calling their office. Later that day, the counseling center's office called our house number and helped us schedule an appointment.. and that's where it all started.