I want to stress again that the best presentations concentrate on examples and not slides. Think about your presentation this way.

1. Decide what examples you want to show and what points/information you want your examples to get across. Organize your examples from simple to more complex. 
    
2. Once you have laid out the sequence of examples, only then think about what information you have to present in advance so that the audience will be able to understand the examples. Usually that's not very much. Perhaps you can say something about the overall problem the system is intended to solve or the overall service it is intended to provide. But for the most part make the introductory section as short as possible.

When showing examples realize that the audience has never seen them before.

• Don't jump around. Let the audience look over the code and get used to it. Don't jump back and forth from one chunk of code to another. If you have to show two chunks of code at once, see if you can how them side-by-side.
   
• Go slowly. Code takes a while to read. Give people a chance. Help them read it. It takes a lot longer to understand code in a programming language, even one you know, than it does to understand the same amount of text in a natural language. 
   
• Point out the part of the code that you want the audience to notice and tell people that they need not bother with the rest. (But be sure the rest really can be ignored -- at least at the moment.)