A lot of users who are unfamiliar with how the Mac OS X and how installing software on it works will go and download some software for the Mac and then wonder “A .dmg, how do I install that?”
Well here is how one would go about installing a .dmg file on a Mac computer.
1. download the .dmg file, normally it should download to the Desktop or your Downloads folder.
2. Double-click the .dmg file that you have downloaded and a new icon with a similar name will appear.
3. A Finder window may open automatically, if it doesn’t double-click the new icon and it will open the Finder window.
4. Copy (or drag n drop) the new icon (the one that appeared when you opened the dmg) to your applications directory.
That is how simple it is to install new software on a Mac computer. You may additionally create an icon for the dock.