When I was thirteen I didn't know about masturbation, orgasm, or ejaculation. I was clued in when at school a boy made a joke by moving his hands up and down on his ribs, then spurting some saliva. By the way, some other guys laughed, I knew he was doing something dirty. Late that night when I was alone at my desk I remembered what he had done, and I tried it on my unit. That slow up-and-down motion gave me a new sensation, it did feel good! I suspected that it must be about what it would feel like sliding inside a vagina. I just kept on, and after maybe ten minutes a very intensely burning orgasm came, and an involuntary contraction of my butt made me rise a little off my chair. My entire penis was throbbing, and I could feel fluid getting pumped, so with my other hand I held it at the base so none would come out. The whole experience of orgasm was a complete shocking surprise. After a minute or so when I relaxed my hold the semen all flowed out. That was also entirely new to me.
All the next day at school I thought over and over about what had happened, and after school on the bus as I got nearer to home I couldn't wait to be alone; my ONLY thoughts were of jacking off, bringing on an orgasm, and ejaculating.