Make a selection on the timeline
To edit, you must first make a selection on the timeline.
Select a portion of the timeline
Press Shift and drag a selection on the timeline.

To edit, you must first make a selection on the timeline.
Select a portion of the timeline
Press Shift and drag a selection on the timeline.

Select a clip
Click on the desired clip.

Select multiple clips
Shift-click or Command-click the desired clips.