Position the Playhead over a video clip where you want to start the effect (top-left), then from the Edit menu choose “Split Video Clip at Playhead.” Or use the keyboard shortcut Command T. A vertical dividing line appears on the clip under the Playhead.

Position the Playhead at the point where you want to split a clip.

To split the clip into more than two parts, move the Playhead to another position in the clip, then press Command T again. Another vertical line appears in this position, dividing the clip into three segments.

The split clip.

Do this as many times as you want.

Select the clip segment to which you want to add an effect, then choose an effect from the Effects pane.