Summarize the following:
After you have filled in the options and the values of your choice, then click on the Create button located at the bottom of the option box. After the process has been completed, the Disk Utility will automatically mount the new image on your OS X desktop, which will be ready to have files added to it. When you have added whatever you want to add to the disk image, you can drag the mounted image to the trash, which will eject the mounted image. The disk image can now be moved between computers and transferred with ease.

Summary:
Click on Create. Add files. Eject the mounted image.