Mom was red in the face when I found it and started asking questions.
I was 13, I think. It was on a Saturday morning and my mom and I were changing the bed linen on all our beds. We got to my big brother's room and I reached under the mattress to pull out the sheet. When I did this, my hand hit something under it. I pulled it out and it was a magazine that my brother had hid there. I opened it and found pictures of naked girls and lots of the pages were stuck together by this light yellow stuff that was all dry. Then I hit this page that was stuck but still wet and gooey. About this time, my mother walked into the room and saw me looking at the magazine.
She first asked what I had but when she got closer she could see what it was. She said 'Give me that' and grabbed for it. I then started asking questions and first ask why Buddy (what we called my brother) had a book full of naked girls. Mom got pretty red in the face and told me that Buddy is that age and that I'll understand more when I get older. But, I still wanted to know more. I next asked what that gooey feeling stuff was. Mom was kind of lost for words but I kept it up. I wanted to know everything.
Then, mom finally told me about boys and there 'equipment' and how they play with themselves and get aroused looking at pictures of nude girls. She then told me about the stuff telling me it was called semen and it had his sperm cells in it which is what makes babies and that it feels real good to your brother when he squirts it. Again; she said I'll understand more when I get older. I could tell mom was real uneasy talking about everything but I did learn enough that morning to know about what I'd later know as cum. Of course, I'm now VERY familiar with the stuff and know exactly what my brother was feeling back then.