Make yourself at home
So you've found and installed a Linux distribution you like. What now? Play around on the desktop to make it comfortable. Set your preferences, choose wallpaper, and check out the preloaded apps. Most every Linux distro comes with a default desktop environment, which determines the look and feel of pretty much everything you see. Most offer alternative options as well. If you don't like your default look and feel, you can swap in numerous others.
The mobile-inspired GNOME 3 is the default desktop in many of the bigger Linux distros, including Fedora, while Unity (also mobile-inspired) is what you get in Ubuntu. A growing number of newer distros, including SolusOS and Fuduntu, display more classic default desktops based on the style of GNOME 2.
If you dislike your default desktop, check out the alternatives. KDE and Enlightenment (E17) are generally considered the most visually appealing desktops, while Xfce and LXDE are minimal and lightweight. This Wikipedia page offers a nice glimpse. Keep in mind that the more similar your distro is to the OS you and your staff have been using, the shorter your learning curve will be.
Get the apps you need
There's no need to waste time searching the Web to find software. Instead, software for Linux is available in what's known as the software repository, similar to an app store. For Ubuntu Linux, that's the Ubuntu Software Center; but for the most part, each distro has its own equivalent (to find it, look in the administrative menu of your OS). Typically, software there is vetted, reviewed, and safe to download.
A tool called the package manager lets you find and download software from the repository. If you're looking for an equivalent to a big-brand, commercial application, OSalt is a good place to start. Wikipedia has a nice list as well.
You'll find user reviews for most of the following apps in the Ubuntu Software Center. For other distros, try Gizmo's Freeware site as well as OSalt. The following popular, free, and open-source business applications will often already come bundled with your Linux distro:
Accounting: Though not open source, QuickBooks is often held up as a reason for not switching to Linux. Its availability in browser-based form removes that obstacle. Also available is the free and open-source GnuCash.
Web browser: Firefox and Chrome are the two biggest options for Linux users. Firefox integrates nicely with Thunderbird for email, but the choice between the two mostly comes down to a matter of personal preference.
Graphics: GIMP is the default graphics package included by nearly every distro, and it's excellent.
Desktop publishing: Scribus offers a user-friendly interface, along with support for professional publishing features such as color separations, CMYK and spot colors, ICC color management, and versatile PDF creation.
Next page: Arrange training and support...