You can follow below two ways to trim the video.
1.Move the red indicator in the timeline to where you want the clip to be trimmed. Right-click (or control-click) on the video and select "Trim to Playhead".
2.Or you can select your video and then hover your cursor over the edge of the video clip in the timeline. Then drag the edge of the clip left or right to trim the clip from the beginning or the end of the video.
If you need to cut a chunk in the middle of the video, you can follow below steps: