The Fill Command

The /fill command is a basic command that is used in high-scale building.

Overview
The /fill command fills an entire cubic area with one type of block.

Syntax
/fill      

Explanation
The /fill command isn't too complicated. The first three values are the coordinates of the first corner of the area you want to fill. The next three values are the coordinates of the second corner of the area. This corner is not the second out of eight corners of a cube. Instead, both corners draw lines on all axis in the direction of the other corner. The lines terminate when they meet. Finally, the block is the type of block that the area is filled with.

Trivia

 * This is similar to the Setblock command, but on a larger scale.
 * It is probably the most useful command when building large structures.