Consolidate Library in Itunes

This button is only in iTunes for Windows. You can read here on Apple's site what the button is for: http://www.apple.com/support/itune [...] 2081b.html

But, basically, what this button does is moves all of the music files that iTunes can find on your computer into a single location. Before you click this button, it might be that all of your music files are scattered all around different folders on the computer. The real purpose of this organization tool is so that you can copy all your music quickly (to another computer or to a hard drive for backup).