One way to store or group files on a Mac is to create a Disk Image. A Disk Image is a file which has the properties of a separate hard drive or CD. It has a size limit and options for encryption to keep your files safe and secure. This how-to will work with Mac OS X.
Create a New Folder and place the files you would like in your disk image into this new folder.
Right click (or CTRL-Click) the folder and select "Get Info" and note the size of its contents.
Open Disk Utility (Applications > Utilities > Disk Utility)
Click the "New Image" icon to create a new disk image. Enter a name for the Image, and select a size adequate for the size of your folder you created in Step 2. Set the encryption to "none" and Format to "read/write disk image." or "DVD/CD Master." See Tips to learn how to encrypt the image.
Place the contents of the folder from Step 2 into the newly mounted disk image.
Unmount the Disk Image by dragging its icon to the Trash. In the Finder window, you can also click the Eject symbol next to the mounted image.
You can encrypt your Disk Image with a password if you would like your files to be private. Simply Select "AES-128" under the "Encryption" drop-down menu. After you click "Create" and it will ask you to create a password for your files. If you add the password to your key chain, you will not have to enter your password to access the .dmg file when logged into your account.
After you add your files to the image, you can unmount it and then click the "Convert" button in the toolbar. This will let you compress the image or change it to read only (or add encryption).
When you double click a .dmg file, it will "Mount" on the desktop. This is the only way to access or modify the contents of the Image.
A .dmg file can be a very easy way to send files from one Mac to another. Any Mac can mount and access the Disk Image on their computer.
To create an image from a folder, drag the folder onto the Disk Utility-icon, or choose "New->Disk image" from folder in the File-menu in Disk Utility.