Transitions indicate you have completed one section or one main point and are moving on to the next.
 

 
Put ideas in order and let the audience know where the ideas stand in relation to each other.

 
At the beginning of a section, previews let the audience know how the points of your message will develop and how they are organized.
 

 
At the end of a section, internal summaries remind your audience of the point you have discussed.