R by itself does not handle GIS type of work but with different add-ons it can be a quite potent GIS device. You'd need to understand the idea of "package" (user-contributed scripts) and how to use
install.packages("whateverPackage") command to install them.
I don't use R in GIS enough to show you the whole topography (pun totally intended), but the most commonly used packages I have seen are
Also, check out some sites and tutorials about this topic: 1, 2, 3, and 4. These got me started and within a day I could make some silly maps.
Lastly, this pdf probably contains some codes pertinent to the map you wish to create. Its $\LaTeX$ format is a bit off, but you can still get some general functionality and key commands.