iMovie 11 is the latest incarnation of Apple's popular video authoring tool. With it, you can import video clips from external devices or from anywhere else, arrange them on a timeline, shuffle them around, and preview the results; when you're happy you can create a final video file suitable for burning to DVD or uploading to share with others.
iMovie 11 has a clean interface. You drag files (video, audio, image) to a project area, and from the file area you drag what you want onto the timeline in the bottom pane, arranging the files in the order you want. You can then preview the resulting video in real time and apply effects. You can also manage audio clips and sound effects the same way. There's a bunch of generic themes you can apply, as well as some neat features new to iMovie 11, such a face finder and the ability to quickly create move trailers. Once it's all done, export your file for iOS or Internet usage.
iMovie 11 works well and competes with packages selling for hundreds of dollars. Sure, those expensive packages have a few more features, but most people will never use them. For the vast majority, iMovie 11 is a great app that's easy to learn and use. You'll be creating blockbuster movies in minutes!