Click every little button (e.g. "The first menu item takes you to the home page. The second button takes you to the contact us page. The third...").

Think about what a user of the system wants to accomplish when using the system, and show that. 

Point out every little feature (e.g. "In the top right we have a login button. Next to this is a button for if you forgot your password, and here is a button to sign up").

Ensure you explain all of the validation which happens in the login form, e.g. "Here we will try to enter a password with only lower case letters. Now watch as I type all numbers and it tells me I need to have a letter. Now I'll try a password that is only 4 characters long").

Think of their user journey and show that.