Introduction to Add-ons
Mathematica comes equipped with hundreds of built-in functions. However, if you work in a specialized area, you may find that you need functions that are not built into Mathematica. You can extend Mathematica's capabilities beyond the built-in functions by using add-ons.
An add-on is a collection of files that define new Mathematica functions. These files may include Mathematica code as .m or .mx files, notebooks, MathLink programs, and configuration files. The terms add-on, add-on package, and package are often used interchangeably.
There are hundreds of add-ons available for Mathematica. Add-ons that are part of Mathematica are called standard packages. There are some add-ons that are for sale by Wolfram Research and also by independent developers. Go to www.wolfram.com/products for a listing of currently available add-ons for sale. Finally, there are free add-ons that are available from many sources. One of the largest of these collections may be found at library.wolfram.com.