Blocking to keep the joists vertical
Joists are the pieces below the final decking that support it. Blocking is just pieces of wood set between the joists to keep them from turning, since they’re only toenailed in (diagonally nailed to the beams). The joists are the pieces running more or less horizontally to the left; there is a piece of blocking about middle right, and the top left corner shows a piece of decking. Weed barrier covers the ground, ready for some gravel to hold it down.