[noob]

The voltages refer to the voltages on your PSU.
They are typically called rails.

Your PSU has several rails, +12V, +5V, +3.3V, -12V, -5V, and +5VSB

Modern Computers typically get most of their power from the 12V. Other devices use the +5 and +3.3V for their power, e.g. DVD drvies, floppy drives, fans, HDD's, etc.

As far as I'm aware the -12V and -5V are more for ground than actual negative voltages (someone else here will know more). +5SB can be used for things like 'wake on LAN', etc.

A decent PSU will have good 'rails' that being stable, with little or no fluctuation between no load, and full loading. Their rails will typically have 15-18A for each 12V, ~15-25A 5V rail, and ~12-25A 3.3V rail.

A modern PSU should have high 12V rail amperages, be very stable under load, and the ratings should be for when the PSU is at an actual operating temp (~60C) not at 20C as most cheap ones are. They are possibly the single most important component, especially if you are overclocking.

Now to put it in perspective. The skulltrail, as reviewed here, consumes less than 500W under full load.
Intel suggest 1000W PSU, not because that's what it will consume, but because so many PSU's out there are rated far above what they should be.

JonnyGURU.com - Power Supply Reviews and more! - News has reviewed many PSU's and if they basically finish his testing they are decent PSU's.