Once you select a clip on the timeline, you will find the following clip editing capabilities that show up:
Let's look at each of these in detail:
Crop: By clicking the crop icon, you can crop or reposition your clip so that it remains perfectly framed on a square, vertical or widescreen video.
Cut or Split: The scissors icon lets you split the clip into two (only in the case of videos).
Delete: And the bin icon lets you delete the clip.
You can rearrange or swap clips on the timeline by clicking on them and changing positions. Here's how to swap clips.
Note: All of these steps can be undone by pressing the 'Cmd' and 'Z' keys or clicking on the 'Undo' button at the top left.