The Preview Frame is the agenda or table of contents for your speech.
Many speakers that are in my public speaking workshops or that I coach one on one have problems rambling on and on in their speeches. Sometimes they get pulled off topic by a question, sometimes they meander from the content of a slide to something they find interesting. What ever causes a speaker to go "off point" the solution is to create a easy method to stay on point. So when you write and give your speech make sure you have a set of main points that support your purpose sentence. The ideal number is three. (see my other blog entry on the power of three) These main points are the outline or agenda of your speech. Following the metaphor in my book Easy Speaking that building a speech is like building a house the main points are the frame work or the house. You state it in the introduction of the speech to give a preview of "coming attractions."

 The is the structure of the house. A preview reveals the presentation’s main points and the order in which they will go. The best way to do this is to say the number of the points out loud so people can easily divide the chunks of information and follow them throughout the speech.
 For shorter presentations:
 “You’ll walk out of here with three ways to prioritize your time.” “When we finish this session, you will be able to list the four most effective public relations techniques.”
 Today you will learn the three benefits of our product.
 For long presentations say what those points will be.
 “. . . And to do this, first, you’ll learn about the early history of the organization; second, of its rapid development; third, about its present stature; and finally, about its prospects for the future.”