Yes, you can copy and paste (i.e. duplicate) video clips and other media clips in the timeline of the Create editor – see below for instructions and screenshots.
You can also make copies of entire projects. To learn how, please see this help article: can I save different versions of my project?
How to duplicate a clip
1. Select the clip (or clips) you want to copy in the timeline
2. Click the copy clips icon (two squares) in the top left of the timeline
3. Position the white bar where you want to paste the clip
4. Click the paste clips icon (two squares + down arrow)
This will create a copy of the clip in the timeline, including any edits (e.g. trims, cuts or filters) you've applied to it.
You can also copy and paste multiple clips at once. Simply hold down the shift key on your keyboard and click on several the clips to select them, then use the copy and paste icons in the same way shown above.