Giving a demo of your application or web site to an investor or potential partner is different from teaching a new user how to use it by herself.
For the user:
Where do all the buttons sit
How to log in
How to update settings
Where to find your account details
How to create a project from scratch
Etc.
For the investor / partner:
What does the app do?
Show me a walk through of a “story” or use case
Have a project ready to show
Look, there is actually a piece of software that is working…
Etc.
In presentations, you are most likely to deal with scenario 2. Do all the prep work (logging in etc.), and design a very clear script of what you want to show, cutting out any tangents and other delays. Keep it short and focused. Rehearse your walk through, and as a backup, have a series of consecutive screenshots ready just in case Murphy’s law kicks in.