Below is a screen shot from iMovie.

(1) The Shelf or Bin

This area is where all of your video clips go.

(2) The Monitor Panel

This is where you see your video. If you have clicked on a clip in the Shelf, you will see just that clip. If you click into the timeline, you will see the entire movie. The blue inverted triangle that shows up when the clip is playing is called the play head. Below that you see buttons for Rewind, Play and Full Screen.

When you are viewing a clip, you can edit it by dragging the two small triangles to the desired start and end (in-point and out-point) and choosing crop from the edit menu. This will remove unwanted areas of the clip. See below where the orange part of the clip timeline is the part that will be kept:

Another (less destructive) way of editing a clip is to place the playhead at a desired location and to choose “Split Video at Playhead” from the Edit Menu. Now you will have two clips in the Shelf. One containing everything that was to the left of the playhead and another containing everything to the right.

(3) The Movie Timeline

This is the timeline of your entire movie. Clips can be dragged from the Shelf to the timeline and arranged in the order that you like.

(4) Clips, Photos, Audio, Titles, Transitions, Effects

Depending on which of these are highlighted, various options will appear above (in the area where the clips are now showing).

(5) Camera or Editing Button

When this switch is to the left, iMovie is ready to import clips from your camera. When it is to the right it is ready for editing.

(6) Timeline views

Depending on which is highlighted, you will see either a clip view of the time line (left selection) or the advanced editing view (right selection).