I saw someone demonstrating the beginning of a sales page. He made the background black and then created a white box and sized it to be a wide area down the center. Then he typed his content on that area. How do I create a box like that in KompoZer?
You will have to place a Text Area form. This can be achieved using Form > Text area. After the option has been activated, configure it. Input additional rows and columns to make it larger or smaller as show in the image below.