Automator OS X Guide
Doing the same simple task over and over becomes really annoying. Automator will do all those clicks for you. Let's say you want to take all the photos added to iPhoto last week and change them into a .JPEG to get them ready for your website. In the first menu, you would choose custom. For your first action, you would want the app to ask you which photos you want to transform into a .JPEG. To do that, click on Photos>Ask for Photos. Drag the "Ask for Photos" to the workflow. Then, still on Photos, choose "Change Type of Image" and drag it into the workflow. In the drop menu, choose JPEG.
After you are done, click on File>Save. On the drop menu, choose application and give it a name. Click on the app and it will ask you what photos you want to include. Choose your selection of images and then click on "Choose". Automator will now transform all those photos into a JPEG.

This is just 1 simple example out of the thousands of possibilities of Automator. If you use your imagination, you could save countless hours by creating little applications that can do the work for you.