Ubuntu Software Center
If you decide to go with Ubuntu as your distribution, you'll pick up most of your applications from the Ubuntu Software Center, an online store for downloading and installing applications and utilities. The Ubuntu Software Center began shipping with Ubuntu in 2009 and subsequent Ubuntu releases have included incremental improvements. The store currently offers numerous free software packages as well as some paid apps. Using the USC is as simple as searching for a program and clicking Install.
By default, Ubuntu comes with a lot of great software, including Mozilla Firefox and Thunderbird (email client), the Libre Office suite, Gedit text editor, and GIMP. Those applications also come with many other Linux distributions; or you can install them after initial setup. You can get a lot of popular third-party software for Linux, just as you can for Windows and OS X; examples include Google's Chrome browser, Skype, Spotify, and Scrivener--a popular word processor designed for professional writers. Much of this software, including Skype, Spotify, and Scrivener, tends to be marked "beta." But don't let that scare you off: All three work very well in Linux.
If you can't find a Linux version of the software you need, you can try running Windows apps in WINE, a program designed to handle that task inside Linux. WINE may not be able to run every program you throw at it. But if you absolutely need a piece of Windows software, and no Linux alternatives are available, give WINE a try.
If you run into problems while using Linux--whether hardware issues, software installation problems, or something else--you can turn to numerous online forums for help. Typically each distribution maintains its own forum where you can seek out assistance, and many third-party sites are full of solid advice, too.
The best way to find help is to start with a simple Web search for the problem you're having. Searches often lead Ubuntu users to the official Ubuntu user forums, but Stack Exchange's Ask Ubuntu is also a good source for information.
When researching problems, you may find that the first few sites you visit may offer complex and over-the-top solutions that require 15 lines of code or mucking about with some file buried deep in your operating system. But chances are that any issues you come up against as a beginner will be comparatively trivial and easy to solve.
Consequently, the best way to research your problem is to assume that it can be solved with a few simple mouse clicks or less than one line of code entered at the command line. There are exceptions to that rule, of course; but if you begin by assuming that the answer to your problem is simple and exhaust all of the straightforward possibilities before moving on to far more complex solutions, you'll save yourself a lot of time and hassle.
These basic tips should help you get started with Linux. So give a few live CDs a try, and see what you think. You'll be surprised at just how useful a Linux system can be.