What do you do if there is some information on your Mac that you want to keep away from prying eyes? Sure you can activate FileVault but that encrypts your entire home folder which for some is overkill. You can also use special encryption software, but why spend money when a good solution is already there in Mac OS X for free?
The solution is to create an encrypted disk image with Disk Utility. A disk image is really a file that sits on your hard drive or somewhere else that really acts as a disk on its own. If you've downloaded software for your Mac you have probably come across many disk images.
1) So go ahead and start Disk Utility (it's in Applications > Utilities).
2) Click on New Image in the toolbar.
3) Select where to save the image, that it should be encrypted, and pick a size. A word of warning: the larger you make your disk image, the longer it's going to take to encrypt it. You can select to make a "sparse disk image" or a "read/write disk image". A sparse disk image can grow as you put more stuff in it, while the other type is fixed size, as far as I know.
4) Now you have a disk image that you can save stuff to. Be sure to unmount the image as soon as you are done with it so that unauthorized users cannot get access to your information.