The easiest way to edit a video I often needed is simply by using ffmpeg CLI tool, rather than using a fancy GUI application it's more practical with a single line of command to output your desired video modification.

# Compress video to get a smaller size (H264)
ffmpeg -i input.mp4 -c:v libx264 output.mp4

# Compress more
ffmpeg -i input.mp4 -c:v libx264 -tag:v avc1 -movflags faststart -crf 30 -preset superfast output.mp4

# Cut video from start to 15s
ffmpeg -t 00:00:15 -i input.mp4 output.mp4

# Cut video from 15s to end
ffmpeg -ss 00:00:15 -i input.mp4 output.mp4

# Cut from 02:15 with 10s duration (02:15 to 02:25)
ffmpeg -ss 00:02:15 -t 00:00:10 -i input.mp4 output.mp4

# Change aspect ratio (stretch/resize video)
ffmpeg -i input.mp4 -aspect 720:540 -c copy output.mp4