Application Bundles
Most applications are packaged into a "Application Bundle", a collection of essential files that are needed to allow the application to run in Mac OS X.   Applications bundles are often provided as a "Disk Image" (as a .dmg file) or as a compressed file, most often a "Zip" file or "Stuffit" file.

 

To initiate an installation, you double-click on the .dmg file, Zip, or Stuffit file.  Mac OS X will invoke an action appropriate to the packaged type.  For example, a .dmg file will be mounted and presented as a Disk Image icon:

In many cases, the mounting action opens a Window showing you the contents of the Disk Image.  Some applications show you a very basic window and some show you a Finder window.  In either case, you will be presented with an icon that represents the Application that is to be installed.  The example shown in this guide opened a Finder Window as follows:


To complete the installation of the application drag the icon to the Applications folder.  In this example, the Applications folder has been placed in the Dock.

Mac OS X will copy the application and once complete, you will see the application icon added to the Applications folder.  When the icon is visible in the folder, it means that the application has been installed.  Note that Apple recommends that you install all Applications in the Applications folder.

Installers
Many advanced applications are installed via an Installer program.  For example, Apple's Backup software is installed with an installer.  Apple Final Cut is installed with an installer, so too is iTunes.  Many third party programs are installed with installers and are often found on the disk/DVD that came with the prrogram.  For example, Microsoft Office for Mac is installed with an installer.  An installer looks looks an orange open-ended box:



Installers simplify the installation process by either presenting you with instructions or walking you through a wizard.  The example below demonstrates the first screen of Apple's Backup application.  Note the items on the left side of the installer.  These represent the various steps for the installer program and are reached via a step-by-step navigation through the installer.



Last Steps
After you have installed the application unmount the disk image or eject the disc.  You can unmount a disk image or eject a disc (CD/DVD) by dragging their respective icons to the Trash or clicking on the eject button in the Sidebar of a Finder window.

If you would like easy access to the application via the Dock, read the Add Items to the Dock guide.

Benefit of Installing Applications in the Application Folder
By having all applications in the Applications directory, a powerful benefits can be realized.  For example, you will be able to easily move your applications to a new Mac by using the OS X "Migration Assistant" or upgrade to a new version of OS X by using the "Archive and Install" option.