You can save as, and or save for web.
Saving for web will make it save as a .gif.

Save As will allow you to change to what ever format you want.
JPG, Gif, BMP, CRR, STK.
That and more that people dont' use. :P

Procedures:
Look at top left corner of your screen
Click file
and then save as.

You should see a .PSD (Photoshop) in a dropdown box, click on the dropdown box scroller I guess, and you can chose what you want from a huge list.

Enjoy.