Use a background
Many of the generators provide a general background over which you can place built-in effects, titles, keys, and clips with an alpha channel. Some are solid colors while others are textures such as wood or stone. Some generators even have animated movement, providing a more interesting background.
Insert and configure a background clip
Drag the playhead in the Timeline to the point where you want to add the background clip.
Open the Generators Browser by clicking the Generators button in the toolbar.
In the Generators Browser, double-click the background thumbnail you want to use.
Select the background clip in the Timeline.
Configure the background (if applicable) using the settings in the Generator inspector.