Insert Editing
Insert Editing is when you replace audio or video (or both) in a sequence that already has been assembled.
To Insert a clip:
Position Playhead (line with yellow triangle) in the Timeline window to the frame where you want to insert. Define your In and Out points in the Viewer window of the clip to be inserted. Drag the insert clip into the Canvas window (this will bring up your insert options) Decide if you want to:
"Insert" the clip. This will move existing video in the Timeline to the right. "Overwrite" with the clip. This will overwrite existing video in the Timeline.