The textbox that appear on the lower-right corner of folder windows including the desktop itself (as well as in a variety of other applications) lets you type in text that is matched to the beginning of each item present.
For the desktop, files and folders are automatically selected if their names start with the characters you type into that text box. This feature allows you to select an item on the desktop, in another folder, and in many other applications (for example, some music players) by typing in the first few letters in its name.
This text box comes up when you start typing; if you want to dismiss it, press Escape (or click elsewhere, including the desktop itself).
