When I was nine-years-old, my best friend was Nick. He was a year younger than me, but much more likely to instigate activities than I was. One summer night, we were camping in a tent in his backyard, when he told me about jacking off. I didn't know what it was at the time, and had not yet had my first orgasm and ejaculation, although I was quite familiar with erections.
We pulled down our shorts and both had erections. He told and showed me how to grab and stroke on himself, which was especially interesting to me because he was uncut, and I had never seen an uncut penis.
After a while, he let me do him, and I let him do me. Almost as soon as he began stroking my cock, I felt like I had to pee. So I told him to stop, and I went outside and tried to pee against the nearby tree, but had no luck. He suggested we go inside his house to get some paper cups, and I did not understand why. He told me so we could come in them. So we got the cups and returned back to the tent.
We played with each other some more, and he explained that white stuff comes out, not pee. Neither of us came that night (as far as I know), but I did have my first come the next day in the shower at home.
I described my orgasm and ejaculation to him later that afternoon, and he confirmed that I indeed had come.
As the summer wore on, he and I often spent the night in a tree house my father had built for me in the backyard. Nick and I invariably found a quick reason to remove our shorts and underwear, look at each other, and eventually jack. He remained hairless all summer, while I had already had a good patch going even at nine years old, almost ten.
I recall one dark night in the tree house, he was on his back on the sleeping bag, and I had been stroking his uncut cock for a while. All of a sudden it got really hard and felt like it was having spasms in my hand. I said, 'Dude, you came', but neither of us could find any fluid. I didn't know at the time that one could have a dry come. We played with each other and ourselves quite a bit from then on, and he eventually began to shoot when he came.
I learned about jacking off that summer, with my best friend, and have enjoyed it ever since.