A word to describe somebody who likes to understand how something works
Solution 1:
The word tinkerer might fit. To tinker can mean "to repair, adjust, or work with something in an unskilled or experimental manner" (Merriam-Webster). It's the "experimental" part that could make it work for your case.
He's been tinkering with cars since he was a kid, and now he's a tinkerer who knows nearly as much as a mechanic. [source]