Two ways...
1 - right click on a clip in the collection and choose 'Create Clips'... it
may or may not subdivide it further
2 - with the clip selected in the collection or on the timeline, move the
preview to show the frame in the clip where you want it split and use the
split icon under the monitor, the 2nd icon from the right.

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PapaJohn (MVP)
> When I import a home movie from a camcorder, MovieMaker breaks it up into
> clips. How do I now take an individual clip and break that up into
> further clips?
>
> Thanks.