Campaigns can be used to link together events, mailings, activities, and contributions under one "umbrella" so that you can track the progress of all your efforts towards that goal.
Campaign Manager is a new feature in CiviCRM which pulls together metrics per campaign, and which allows for developing campaign trees (hierarchies). It also provides for the concept of 'campaign expenses.
The QuickGuide can be found here.
An example Campaign 'dashboard' (which needs some data to show and we are working on that) can be found here for the Wilton By-Election.