Many Linux distributions provide software "repositories" so that you don't have to search the Internet for software if you want to install something you don't already have. (Listen to Episode 3 and Episode 13 of the podcast for an audio description of using package managers to install browser plug-ins and other software. Note that the CNR repositories no longer exist.)
Although it is possible to control where applications are installed with Linux, it's not something you want to do. For more informaiton about where sofware applications get installed on your Linux computer, see our article: Installing Linux Software (Applications).
The concept of software repositories is likely not all that familiar to users switching from Windows, since you normally have to go to a store, or go on-line to purchase new software for the Microsoft operating system. With Linux, almost everything that is available and tested for a specific distribution of Linux is available in the on-line repositories for that distribution.
Unlike the various shareware websites for Windows add-ons, software repositories for Linux are managed, maintained and updated by the Linux distribution, and contain almost ALL of the full-featured, free and open source software, that has been tested for installation on that particular distribution. (And they won't put spyware and viruses on your computer!)
To be clear, in the Linux world, software packages are often referred to simply as "packages."
Most newbie-friendly Linux distributions -- like Ubuntu and its variants, as well as Fedora, openSuSE, etc. -- provide a graphical package manager that automates the process of installing software packages from the repositories. All distributions allow you to install packages from the command line, but since our reading and listening audience is made up of a significant number of newbies, we'll confine our discussion to the graphical methods.
First, we'll describe how to get to a place where you can search for packages in three graphical package managers. From there, you can search for the software package you want to install. If it is there, you will be able to install it easily. If not, you may need to add additional repositories for your package manager to search. If worst comes to worst, you could carefully follow the Linux installation instructions given on the software developer's website. That may (and usually does) involve some command-line stuff. In addition, when installing software not in a repository for your distribution, you could run into installation troubles you don't expect. So it's definitely preferable to install from a repository whenever possible.
Here are some links to information about using the repositories for four popular newbie-friendly distributions:
Kubuntu, and other variants of Ubuntu, are all based on Debian Linux, and use Debian versions of packages. (By the way, if you end-up searching manually on the Web for packages that are installable on your Debian-based distribution of Linux, the package versions that end in ".DEB" are the ones that are meant for your version of Linux.)
Kubuntu 8.04 is our example. Kubuntu provides the Adept Package Manager for installing new software packages. In Kubuntu 8.04 and earlier, using KDE 3.x, Adept is usually available from Kubuntu's System selection in the K-Menu. In Kubuntu 8.04 and later, using Kubuntu's out-of-the-box KDE 4 menu configuration, the Adept Installer is available from the Computer tab on the Kickoff menu.
OpenSuSE and many other Linux distributions use RPM packages. Although the file extension ".RPM" stands for "Redhat Package Manager," the package manager used by openSuSE is NOT called the Redhat Package Manager. It is called YaST -- Yet Another System Tool.