How to go about teaching my son about puberty/bodily changes?

I’m a 27 year old single mom with a 12 year old son (Yes I had him at 15). Ever since I left my abusive relationship with his father, he hasn’t had a male figure around, and I haven’t really had a full on discussion about him about puberty or hygiene/shaving down there. I think he’d probably be most comfortable discussing these things with me even as his mom compared to his grandfather or my brother/his uncle, just because of how much closer we are. I’ve done some research online about male puberty, hormones, and hygiene for uncircumcised boys, but how do I approach having this conversation with him without making him uncomfortable and what else should I talk to him about?

Edit: Thanks for the advice, he was surprisingly comfortable talking to me about some of these things. I took some of your advice and had a casual approach, made a few jokes as well.

Though one thing he confessed was that he isn’t able to pull his foreskin behind his head yet, is that normal and how should he keep himself clean if he can’t expose his head?