"An Introduction to R" could be a good place to start along with the other manuals: http://cran.r-project.org/manuals.html (I think you can also access these through the help menu when interacting with R via the GUI.)

Also, to make nice looking plots, you might as well dive straight into Hadley Wickham's ggplot2 once you've gotten through the very basics: http://had.co.nz/ggplot2/