(All these questions only pertain to Glitchless category)

1. Can someone explain/link me to something that can explain Demo's? Not sure what purpose they serve or what they are.
2. Also, I'm running on the most currently updated version of Portal. Is this not recommended? (Also, not using relaxation vault skip save)
3. If I add footage captured through OBS is that sufficient proof for a run? I currently have a PB of 21:37 but can't post it because all I have in the way of proof is a screenshot of the end of the run and my saved PB in my Live-split. Obviously this won't be accepted so before I run again I'd like to know what I need before hand.