A blocking board is a great tool if you are crocheting granny squares that you want to have a nice and even result. The board ensures that all your squares are the same size and shape, making assembly easier. 

The board is made of wood and has a MYO engraving in the center. Note that you will need to get a bunch of nails or similar to tighten the corners. The board has markings for centimeters (see picture). 

Before you start blocking, gently dampen your squares (too wet squares can damage the wood). Once you have blocked them to the desired shape/size, let them dry thoroughly before you sew or crochet them together. Avoid placing your blocking board in direct heat as it can damage the wood.