Every document, program, folder, and disk on your Mac is represented by an icon: a colorful little picture that you can move, copy, or double-click to open. In OS X, icons look more like photos than cartoons, and you can scale them to practically any size.
An OS X icon’s name can have up to 255 letters and spaces. If you’re accustomed to the 31-character or even eight-character limits of older computers, that’s quite a luxurious ceiling.
If you’re used to Windows, you may be delighted to discover that in OS X, you can name your files using letters, numbers, punctuation—in fact, any symbol except the colon (:), which the Mac uses behind the scenes for its own folder-hierarchy designation purposes. And you can’t use a period to begin a file’s name.
To rename a file, click its name or icon (to highlight it) and then press Return. (Or, if you have time to kill, click once on the name, wait a moment, and then click a second time. Or—new in El Capitan—right-click the icon; from the shortcut menu, choose Rename.)
In any case, a rectangle appears around the name (Figure 2-2). At this point, the existing name is highlighted; just begin typing to replace it. If you type a very long name, the rectangle grows vertically to accommodate new lines of text.
If you simply want to add letters to the beginning or end of the file’s existing name, press the or key after pressing ...