Wooden Building Blocks tend to start out as the child's first building experience.  The first thing they do is simply stack them one on top of each other, as tall as they can. Then either they fall on their own or the child knocks them over with the biggest smile or laughter. This is exciting to watch and remember for a lifetime.  The second is they start to build something that only their imagination and ingenuity understands.

As they continue to build to the diagrams in their minds, they start to learn relationships about the blocks. This is a size/color relationship where we call them a unit building system and the color is given to a block based on the length of the block.

As the child continues to build, they learn that if they use a particular color to make a wall (or similar item) by standing all of those particular colored blocks on end, that they are the same height. When they run out, they start to substitute other colors and find none are exactly the same. So they start to combine multiple blocks of different colors or combinations there of to equal the same height of the original color. 

Once the child learns some of these relationships over and over, they will use the concept they have learned to build more exacting and with much more precision.  These relationships of the building system are really nothing more than mathematical relationships. Substitution of a number for a color can be a simple process for adding and subtracting.