I feel like I have no idea how to do this. I got some nappy training pants today. But our problem is that while he will go to the toilet pretty much every time we put him on it, he's too little to tell us when he needs to go.

Do I just put him on really regularly and hope he learns to hold it in?
What i would suggest is when you are ready let your DS run around nappyless so he can start to feel what it's like to wet. So that he can then relate the feeling of needing to go, to wetting himself and then knowing that the feeling means to run to the toilet. That's how it worked with us. It took us forever to have DS1 finally do a wee on the toilet.

That's why in my previous post i was so excited to have DS2 stand outside, hold himself, aim and wait a few seconds for a wee to come!! From my past experience that's a huge breakthrough!!

I also suggest lots of talking about it and showing him how it's done, but not in an overly forceful way