To import video into iMovie for editing, plug your camera into the firewire port and put your camera in playback or VTR mode. Then, make sure iMovie is ready to import video by switching the Mode Switch (the Mode Switch is below the main monitor window and the scrubber bar on the left) to camera mode. While in camera mode, use the playhead controls to preview your movie and to decide the point at which you want to begin importing. It's best to start playing the movie slightly before the point at which you want to begin importing because it's quicker to crop extra footage than to import and add in more footage. Then, while playing the movie, go to the File menu and select Import. To stop importing, click the Import button again. You can also start and stop importing by hitting the space bar.
By default, imported clips are stored on the clip shelf. You can change this default by going to the Edit option, selcting preferences, and then Import. You can change the default to have the clips import to the clip shelf or the clip viewer.