I went a few months ago when I was still seventeen, my GP didn't even mention my parents at all, even when I told him I was Self harming and considering suicide. My parents didn't even come into it, although all GPs are different I suppose and some might want you to get your parents involved but I'm pretty sure they aren't supposed to say anything to them and tbh I can't imagine they would if your 17.
Well done and good luck for deciding to make the appointment, you really won't regret it. It helped me so much to finally get some help from sombody when I was at my lowest point.
My GP just asked me some questions about my general mood, eating/sleeping habits, any thoughts of harming myself (or actually harming myself SI) ect ect. He did a questionarre for me and reffered me to a counciller and then a phychiatrist and also prescribed some anti-depressants.
Good Luck, I think it's a reeally good idea to do this and it's brave of you to get help! xxxxxxxxx