The call to action is the 'thing' you want your audience to do (action to take) as a result of your having provided them with compelling facts, argument and stories (provided in the body). The call to action is typically located in the conclusion but could be a 4th argument prior to the conclusion.

In short: The call to action should activate the listener to complete an action or mission, or adopt a new way of thinking or living their life. Be sure that the Call to Action is clear and simple to understand and do.