Small parts of something bigger, like pieces of a puzzle.
Subblocks are important because they help make the bigger thing work.
Examples:
The Lego set has many subblocks that you can put together.
She needs all the subblocks to finish the puzzle.
I found the missing subblock under the couch.
The subblocks are hiding in the box.
The subblocks are so tiny, they're like little secrets.
The subblocks are the key to finishing the big project.