Why "Start Time" and "End Time"?
Videos are long. You usually only want a specific highlight (like a 10-second clip from a 2-hour stream). By setting a Start and End time, you tell the computer exactly which part to cut out.
What is an Audio Track?
Think of audio tracks like layers in a photo editor. You might have one layer for your microphone and one for the game sound.
OBS often records these separately so you can edit them later. This tool lets you choose which "layers" to keep in your final video.
Why "Copy Original Bitrate"?
Copy (Fast): Like using scissors to cut a tape. It's instant and doesn't lose quality.
Convert (Slow): Like rewriting a book by hand. It takes time and might introduce small quality changes. Use "Copy" unless you have a specific reason not to.