You can import slides into your presentation from outside files by going to the Insert|Slides from File menu.

Use the Browse... button at the top of the screen to select the other presentation. At the bottom, the Slide Finder will list all of the slides in that presentation. Click on the slides you wish, or click the Insert All button. When you choose the slides you want, they will adopt the slide backgrounds of the original presentation.

You can also import an outline that you made in a text document. The Insert|Slides from Outline option allows you to take an outline from a text document, such as Word or WordPerfect, and make slides out of it. It should be noted that the import works best when you use the [TAB] key to create different outlining levels.