This is not so much how I got started in BDSM, but more of when I 'awakened' to the fact that I liked it when females had power over me.
I was interested in girls from a much earlier age than that of my peers. My 'best' friend was actually a girl, slightly older than me, and most definitely confident and self aware. From a young age I had a desire to tied up, and as I got older toward my eleventh birthday I took every opportunity to explore this; in group games I was always the one 'captured', and tied up in the tree house. The other kids seemed happy about this because they wanted to run around and join in; whereas I was quite happy to be the captive tied to a post and kept secure while the game played out. My 'best' friend, Anna, nearly always did the tying as I could escape when the other kids tied me, but Anna really knew how to secure me so I could not escape, and even make it uncomfortable enough so that I would beg her to let me out. Looking back, I think in some strange way she also enjoyed our games, there was no 'touching' or blatantly sexual element, after all we were still kids; once she had me tied she would sit down next to me and we would talk about general kids things as though nothing had happened.
A major trigger for me occurred one summer evening when there was only Anna and myself in the tree house. Anna was a physically well developed girl for her age, she was self conscious of her developed breasts and did not like it being mentioned as few other girls her age were as well developed as she was. This evening, she asked me if I wanted to be tied and I said yes, of course I did. She told me it would be tight and I had to be brave; she then proceeded to tie me in what can only be described as a stress position with my arms and legs stretched wide apart. It started to hurt quite quickly, and I asked her to let me go. She refused, reminding me that she did not let me go until she was ready. I got angry with her and called her some nasty names, making reference to her breasts. She in response got angry, and slapped me square across the face. I was a lot shocked; she kind or recoiled back and said she was sorry, very quickly followed by indignation 'but you deserved that'. I just stood there, I didn't know what to say, my face hurt, but somehow I liked it. I felt a wave of emotion come over me; conflicted, not wanting to feel the pain of a slap, but wanting her to be cruel and hit me again. I mumbled to please let me out, I was hurting, she stood in front of me and said firmly 'no, not until you say sorry'. I hesitated and she rose her hand back as if she was going to slap me again, giving me a look as if saying 'what is it going to be'. I just looked at her and noticed her body language, her pose, and I just knew she was going to slap me again, so I looked directly at her and held my face still, and without talking, daring her to do it. She slapped me, good and hard, it brought tears to my eyes and I broke down apologising profusely, begging her to let me go. She looked triumphant, announcing that I had learned my lesson and she then untied me.
This is my earliest memory of actively wanting to be dominated and coerced by a female who had power over me.