Wood

 is a very easy resource to replenish and very abundant at the start of the game, being light brown in colour, it is obtained from cutting down trees by using any axe in the game. Wood Blocks are required at the start because they can be crafted into many useful items that are required to progress through the game, like a Workbench.

It is a recommended building material because it is abundant, easy to replenish and drops in a large quantity for every tree.