One block is set on top of another. Another block is set on that one. The tower rises slowly, different colored cubes of wood resting on one another, close but not glued together, balancing. There’s a point when the tower will topple and will need to be built again. The trick is to add blocks at the bottom, on all sides of the first block; the taller the tower, the wider it should be made with the aid of supporting blocks on all sides.
The support is key.