-codec copy tells ffmpeg to pass through without re-encoding (copy the existing codecs, audio and video)
-ss hh:mm:ss.xxx the starting point in original_video_file.mp4 from which you wish to cut
e.g. -ss 00:11:30.000 to start from the eleven minute and thirty second mark in the video
-t hh:mm:ss.xxx time, or length of the video from the start point you wish to cut
e.g. -t 00:12:25.500 will cut a section of video twelve minutes, twenty five and a half seconds long, starting at the point indicate by -ss
NOTE: if the video is shorter than the start time plus the cut video length,(-ss hh:mm:ss.xxx + -t hh:mm:ss.xxx) ffmpeg will simply produce a shorter video, finishing at the end of the original video
output_video_file.mp4 the name of the created cut video
Notes
ffmpeg will leave the original file in its original form