Campaigns are generally used to help you monitor your marketing efforts for your web site. Common types of marketing for most sites would be either ads on search engine result pages, and/or social media.
There are two different ways to track campaigns with Clicky. The easiest method is to use the dynamic "UTM" parameters that Urchin / Google Analytics made popular and are now supported by most analytics services. The other way is to pre-define landing pages on Clicky that are generally only used for inbound marketing purposes. These are called static campaigns.