The default statistical computing package will be R and its web interface Rweb, which can be used in any web browser. If you are familiar with another computer statistics package, you may use that, but the instructor and teaching assistant may not be able to help you with it.
R R is a general purpose computing language designed especially for statistics.
You can do any computational problem in R, but what it is really good at is statistics. Unfortunately, the Macintosh port seems moribund. You do not have to download it if you don't want to. The textbook describes using R to do all the statistics it covers. You have to fill them in to get any work done.