R Interface
R can be downloaded for free at http://cran.r-project.org/ .
Once you've followed all the installation instructions, you can double-lick on the R-icon on your desktop (if you have a windows machine) or from your applications folder (if you have mac).
The new releases of R often come with two options: 32 bits or 64 bits. It does not matter which one you choose to open.
The R-interface looks like this.
R-commands can be entered one at a time at the command prompt (>) or run a set from a source file.
Note: R is case sensitive.