Free software includes at least a dozen mail readers, but the most common ones are GNOME's Evolution, KDE's KMail, and Thunderbird, a companion application to the Firefox web browser. For those used to Outlook, Evolution will seem the most familiar, with its built-in contact lists and memos, but all three applications are broadly similar in features. Thunderbird is especially popular, since it is also available on Windows.
No matter which mail reader you choose, enabling your email is straightforward so long as you have the necessary information. Both Evolution and Thunderbird include wizards to guide you, but, if you work systematically, KMail is almost as easy to install.
Once you have installed a mail reader, you may also want to spent time configuring its message filters for directing mail into different folders and identifying spam.
GNU/Linux desktops are improving constantly. However, in keeping with free software ideals, many distributions choose either not to ship with proprietary software, even when they increase functionality.
You should decide early on whether you want to experiment with proprietary elements or not. Probably the most commonly used proprietary software are video drivers for ATI or NVidia cards. For office productivity, you don't need to bother, but if you are a gamer, animator, or CAD user, or would like to try compositing window managers -- in short, if you anticipate doing anything that needs 3-D acceleration -- you may want to investigate the proprietary video drivers.
Other proprietary elements you might want are the MP3 and Win32 codecs for audio and video formats. By contrast, you can probably get along with the free PDF readers. And, for many purposes, Gnash is starting to become an acceptable Adobe Flash reader, and the free versions of Java adequate replacements for Sun Java.
Some of these proprietary pieces may be in your distribution's repositories. In other cases, depending on the piece or the distribution, you may have to go to a specific download site or an unofficial repository. Nose around on your distribution's mailing lists to find the sources you need, but remember that unofficial repositories can sometimes cause compatibility problems that will require long hours of work to track down and fix. Consider these problems the price you pay for compromising on free software ideals.
Many GNU/Linux installations are on dual-boot systems, with a boot manager that opens when you start the computer from which you choose to boot Windows or GNU/Linux. If you regularly switch back and forth between operating systems, you will probably need to decide how you will share files.
From GNU/Linux, you should have no trouble reading files on Windows. In fact, many distributions will have set up the ability during installation. If not, create a sub-folder of the /mnt directory (the traditional place from which to access other partitions), and use the mount command to access your Windows partition. The only complex part is the name for the partition, but, these days, it is probably /dev/sda1, so the typical command would be: mount /dev/sda1 /mnt/share. To save yourself the need to use the command, you can have automatic access to your Windows partition by editing the /etc/fstab file, which lists the partitions that are made accessible every time the machine starts. The command man fstab should give you all the help you need, but plenty more help is available on the Internet if it is needed.