After you've put a ton of work into whipping up a lovely creation, don't forget to save it or you'll never see it again. As in any program, be sure to save early and often so your efforts don't go to waste if your computer crashes or the power goes out.
The simplest method is to choose File→Save or press ⌘-S (Ctrl+S on a PC). If you haven't previously saved the file, Photoshop summons the Save As dialog box so you can pick where to save the file, give it a name, and select a file format. If you have already saved the file, Photoshop replaces the previously saved version with the current version without asking if that's what you want to do. In some situations, that's fine, but it can be disastrous if you were planning to keep more than one version of your image.
You can play it safe by using the Save As dialog box instead; it always prompts you for a new file name (see Figure 2-4), which is handy when you want to save another version of your document or save it in a different format. Choose File→Save As or press ⌘-Shift-S (Ctrl+Shift+S on a PC) to open the dialog box. From the factory, the Format pop-up menu is set to Photoshop, which is good because that format keeps all of your layers intact, as you'll soon learn. But, as the next section explains, you can save files in lots of other formats, too.