In R statistical procedures are organized into groups of related functions and are called *packages*. The base version of R ships with built-in packages, which are loaded by default when we start R. Many more functions, which drastically extend the functionality of base R, are available from packages developed by users in the R community (contributed packages). Anyone can write and upload a properly formatted contributed package to the CRAN servers.

In order to download a contributed package and make use of therein provided functions, we have to type `install.packages("PACKAGE-NAME")`

into the R console (Note the quotation marks!). For example, in order to download the quite popular `ggplot2`

package, a package for data visualization, we type

`install.packages("ggplot2")`

Once downloaded, we can access the bundle of new functions within R by typing `library(PACKAGE-NAME)`

. Note, that this time we write the package name without quotation marks! With respect to our example from above, we write:

`library(ggplot2)`

If everything worked out fine and we do not get any error messages, all the functions of the `ggplot2`

package are now available within R. It is worth noting that in some cases you do not want to load the whole package, but you just want to use one particular function of a package. If you already downloaded the package, you may access function of a package by using the `::`

operator in the form of `PACKAGE-NAME::FUNCTION-OF-INTEREST(...)`

. With respect to the example from above, we make use of the `ggplot()`

function from the `ggplot2`

package by typing the following command into your R console.

`ggplot2::ggplot(...)`