Installed Packages

To find out what packages are already installed use
library()
To find out more about a particular package use library(help=FOO). So to find out more about the stats package use
library(help=stats)
To find out the details of a particular function in a package use help(FOO, package = PKG). So to find out about the lm function in the stats package use
help(lm, package=stats)
or
?lm
The help window displays information about the function in the right pane, and lists all other available functions on the left.

If you need to find a package that provides a particular function use help.search(“keyword”).
So to look for packages that provide regression functions use
help.search("regression")
or packages that will fit linear models
help.search("linear models")
In all cases a new window will open displaying a list of matches. Again the help(FOO, package = PKG) command will describe what the functions available in that package will do.

All R commands that can be typed in exactly as they shown are displayed in red.

The word FOO is often used within R (and in many other computing contexts) as a way to indicate that FOO should be replaced by a real instance of something. In this case a function name is needed. Technically, I believe FOO is used as a metasyntactic variable.