Gundam W is a sub-series in the world of Gundam. It has been assimilated into the world of amerime by Toonami. It has fairly good animation, and good mech-designs.
The plot is just the same as always, fighting, and with some subtle romance, and maybe even a love triangle. Its yet another part of the Gundam world, but adapted for American audiences.
If you need to watch it, try to find japanese versions, or even a fansub. It is far better than the amerime version, as much was edited out.