Initially, I wanted to give our oldest one big lecture and cover everything in one session.  But I recognized that discussing the topic of sex was just as uncomfortable for him as it was for me.  The way I approached it was to give a little bit of information at a time based on my boys' age and comfort level.

Some conversations I would start with a question(s).

“Do you understand why boys and girls are different?”

“Is there a girl you like in school?”  "What is her name?"  "What do you like about her?"

In other conversations I would be straightforward.  Here is beginning of conversation with Grant.

"Grant, it's time to have that talk about sex again."

"Ah dad, do we really have to?”

“Yes, it’s my job as your dad.”

“Okay, but can we use a different word than sex?”

In my sex talks I also included rules about how to respect girls, how I expect him to behave, how to ask a girl out on a date, act on a date and build a relationship with her. Whether he follows through or not is a different story. But at least I did my part as his dad to address the topic and give him my input and some direction.

Honestly, I think much of what my boys learned about sex came from their friends, health class or figured out on their own. What I hope they learned from me was developing the comfort level to talk about it and to know I'm also comfortable talking about it.

Good luck.