You are trying to install or open an app that didn't come from the Mac App Store but you got a message saying App can't be opened because it is from an unidentified developer. This is how you bypass it.
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.
A really useful feature in case you want to receive a warning notification before you use all of the mobile data available according to your mobile provider contract. It's a great way to avoid additional charges.
If you are more of a visual person and would like to organize your folders and files using different colors, than check it out how to use color labels in Mac OS X.
If you experience an Mac OS X program to freeze and you cannot exit it by clicking quit or using a keyboard shortcut, you can always force it to quit using the Activity Monitor.
Let me show you how to achieve that Depth Of Field effect known from the photography using Gimp. With other words, how to make selected area of the photo sharp and the rest out of focus.
