Some installations or settings changes require you to restart your computer. In most cases you don't need to actually reboot it, you only need to restart the explorer.exe process.
Windows 7 have a nifty feature which combines the windows of opened applications under the same taskbar button. If you don't like it you can always turn it off.
By default Windows calculator doesn't support order of operation, to enable the functionality you need to activate the scientific view, let me show you how.
If the DVDs, USB sticks, phones, cameras or any other media and devices are automatically starting to play or open explorer windows and your don't want them to, this is how you tweak the AutoPlay settings.
In this day of age, it's very practical to have a Windows 7 installation on your USB key, for many netbooks and devices don't come with CD/DVD drives anymore.