This is how I learned about masturbation years before I would ever do it myself.
When I was 10 my only brother who had turned 15 at that time got as a birthday present a room of his own. It wasn't a surprise because he had helped prepare the room that was to be used as his bedroom.
I knew for a month that the time was fast approaching when I would have to sleep alone but I wasn't prepared. I stayed up most of the night being worried about different sounds that I would hear and things I would imagine. It was past two am when I got up and walked into the living room and from there I could hear that my brother was still awake I went to his door and I could tell that his light was still on. I walked in to find my brother on the bed masturbating and making all the sounds that came with it.
When he saw me he told me to close the door and I did. I stayed in the room and asked what he was doing and he said 'not now' and continued.
I had seen my brother naked before but not when his penis was stiff and swollen. He kept going at it making contortions with his face that I had never seen and grunting, moaning and breathing like I had never heard.
Eventually his legs stretched out and his toes spread apart and he started saying things like 'Oh baby, oh baby, it's cumming.' When he said that he unloaded a bunch of thick white semen. When he was done he looked at me and asked if I couldn't sleep. He was so matter of fact about the whole thing even when he asked me to give him a box of tissues to clean up.
I of course asked what had just happened and he seemed surprised. 'Haven't you had sex ed?' 'Yes a little' 'Well it's just semen and now you know what the book is talking about. When you put lotion on your hand and do what I did it feels like a pussy and you shoot out semen because your dick thinks your making love.'
That experience right there answered more questions for me than any text book ever could.