Your dog putting it's head on you can be that the dog just wants to be close to you and is showing you that the dog loves you.
Or the dog just loves to lay it's head on you and is comfortable laying down with it's head on you.
The dog is usually either just comfortable laying it's head on your or comes up to you and lays it's head on you because of affection.
It's essentially meaning that the dog loves you and is showing it's love for you and wants to cuddle as well.
It's a great thing when a dog wants to lay their head on you or put their head on you.