Music and Sound Effects: This panel enables you to access audio clips from your iLife and iTunes libraries. To use audio files from other sources, just drag them directly onto the clip in your project where you want that sound or music to start.
Photos: This panel helps you access images in your iPhoto library. To use image files from other sources, just drag them directly into your project where you want that image to display.
Titles: This panel allows you to add animated text and title screens to your video. Hover your mouse cursor over a title to preview its animation. Then click and drag the one you want to a spot in your project. As soon as you drop it down, you will have a chance to edit the text of it. Titles and text can be very useful, but don't overly rely on them to tell the story. Instead, use action in your video to convey the ideas.
Transitions: This panel gives you options for adding animated transitions between clips in your project. Common ones are the simple Cross Dissolve and Fade to Black. Remember that you don't have to use a transition between every single clip. The straight cut (with nothing fancy between the end of one clip and the start of the next one) is by far the most common type of transition in TV and movies.
Maps, Backgrounds, and Animatics: This panel gives you access to a number of specialized motion graphics elements, such as 3D maps of the world and animated backgrounds