I have a little boy, my second one, who enjoys tinkering with things. He finds joy in assembling objects or putting things together -- with his hands.
He is a very purposeful little boy who wants to understand why he needs to do things first before actually doing it. He often asks, "what is it for?" or "why again will i do it?"
If you explain it well enough he will say "aaahhhhh" and will jump right into it with much gusto.