Import your footage into After Effects
Drag the clip into a composition
Move the playhead to the point where you want to cut
Select the layer you want to split
Press Ctrl+Shift+D on Windows or Cmd+Shift+D on Mac to split the layer
Move the playhead to another point if you need a second cut
Repeat the split shortcut to make more cuts
Delete any unwanted split sections
Trim the layer start or end by dragging the layer edges in the timeline
Use the Work Area to define the section you want to keep
Export the final composition when finished