From the webpage:
ggplot2 is a plotting system for R, based on the grammar of graphics, which tries to take the good parts of base and lattice graphics and none of the bad parts. It takes care of many of the fiddly details that make plotting a hassle (like drawing legends) as well as providing a powerful model of graphics that makes it easy to produce complex multi-layered graphics.
I have a few posts about ggplot2 but this site is the mother ship of information on it. Use other resources as necessary but this looks like the canonical source. (Plus you can download a local copy for your laptop. For the odd occasion when you are off net.)