You can use the same video in a project as many times as you want.
By copying and pasting video:
In the Project browser, select video (one or more clips or a frame range) you want to use again, and then choose Edit > Copy, or press Command-C.
The Edit menu appears in a light gray bar across the top of your computer screen.
Move the playhead (the vertical red line) to where you want to add a copy of the video you selected, and then press Command-V to paste the video.
If the playhead is over another video clip, the clip is split in two and the copied clip is pasted in between.
Repeat step 2 to add more copies of the video.
By Option-clicking a video clip:
In the Project browser, Option-click a video clip and drag it where you want the copy to appear in the project.
You can drop it before, after, or between other video clips. You can also drop it on top of another clip. Release the mouse button when you see the green Add (+) symbol, and then choose an option from the menu that appears.
You can also add the same video by selecting it in the Event browser and dragging it to your project again.
When you use the same video more than once in a project, the space used by the project on your hard disk doesn’t increase. The project simply contains multiple references to the same source video, rather than including actual duplicates of the video.