You can use Video Trimmer to trim video clips captured with your Lumia device by selecting start and end points for the clip.

To select start and end points for a clip in the trimming view, just drag the start and end indicators below the video preview.

To preview the trimmed result, simply tap the play symbol.

After trimming and saving a video clip, it is saved in the Saved Pictures album that can be accessed with the Photos applicaton.