What Is A Conditional?
These Conditional options are based on WordPress Conditional Tags which allow you to specify where you DO and DO NOT want your content to display. So by specifying is_page(), for example, you are saying I want my content to only display on your WordPress Pages (ie. not Posts, not Archives, etc..).
The Custom Conditional options, in conjunction with the Custom Widget Areas and Custom Hook Boxes features provide you with truly unlimited possibilities when it comes to displaying your content.
How To Use...
It couldn't be simpler. Just give your Custom Conditional a name and tag value and then click the big, blue "Save Changes" button and you're done. Then, when you're creating new Custom Widget Areas and Hook Boxes you can select different Conditionals to help fine tune the location of your content (if you do not select any Conditionals when create a Custom Widget Area or Hook Box your content will display on ALL pages by default).
To make things even easier for you we've provided you with an "Examples:" drop-down list to help get you started. Just select a Conditional Example and it will automatically fill in the values for you!
Learn more here: WordPress Conditional Tags