The number after the letter V tells you how many cylinders there are. Each cylinder has a single piston, and each cylinder has its air-fuel mix once per cycle of the engine.
The letter V tells you that the cylinders are set up in a V-shape, pointing off in two directions. This layout allows for twice as many cylinders in an engine half the length of an inline engine, usually marked with an I, like I4.
Flat or boxer engines open up that V until the cylinders are directly across from each other. That makes the engine short in length and lower in height, though it does make it wider.