If you want to delete a single clip, here's how:
1) Select the clip you want to delete, click on the three dots on the top, and select Delete from the drop-down menu. You can also select the clip and press Delete on your keyboard.
If you want to delete multiple clips, here's how:
1) Select the clips you want to delete by highlighting them. A black toolbar will pop out; click on the Delete button. You can also select the clips and press Delete on your keyboard.