If you plug something into it, say a fork, and provide a path for current to flow, then work gets done. In the case of the fork, the work is your body moving away at a rapid pace and cursing loudly. Because more is better, we usually refer to kilo Volt Amps, KVA, or kilowatts, KW, unless referring to light bulbs. Generation, transmission, and heavy power utilization of AC electric energy almost invariably involves a type of polyphase system. Because electricity is generated by things that rotate, voltage phases are created as the generators go around.
Phases allow for more efficient generation and distribution of large amounts of energy.
Multiphase distribution equipment is more expensive to install, and after you reach a certain load size, it becomes problematic to implement anything other than a single-phase solution. I will discuss single phase, which covers computers and all consumer electronics, and 3-phase, which is most likely used in your facility to distribute power. This feed powers the whole facility, not just your data center. 12,470V is a common voltage for building distribution. 480V is less common, but not uncommon.