Big welcome to Susan's Fernswift
I told a GP, well after years of keeping it inside me, I just blurted it all out, my emotions just overtook me! Wasn't hard, just seemed it up front. Best thing is be honest, be yourself, tell why and how long you have felt the way you do.
As far as first steps... probably have a good look around our site here, then try and get some time with a gender therapist/counsellor... they will help you with your journey. As far as a GP goes, they will also be able to help you get the basics sorted, as long as they have some experience or contacts into Gender practitioners.
Best wishes and good luck.. also look forward to seeing you about the forum's
L Katy