Hey baby, welcome to the never never land! At least you are so young and whole life awaits you.
You have won already! Confronting dysphoria at your age makes for greater chance of happiness and wholeness in the near future. As to the results of transition, starting at 18 you are nearly guaranteed 100% full passability and if endowed with good genes you might even be a looker.
Now as to your original question, transition in its self encompasses multitude of small details but overall individual is pursuing such to cure the disconnect between brain and body sexual characteristics. Even though it is often referred as sexual characteristic, the feeling of being a woman or man in clinical approach goes deeper than mere sexuality and starts at the core of identity. HRT has tendency to separate physical sexual craving and identity into separate, easily observable behaviors. So in the essence, you want to know if your desires are set on by sexual stimuli or dwell within your identity as a girl. There is nothing wrong with being confused and just to make you feel better most of us had another 20-30 years of this prolonged confusion to finally come to the same conclusion at the end.
I wish you wonderful experience with your therapist and that you may clear your mind and decipher who you are, all my love, Alexia