It looks like you’re going to be bottle conditioning by adding some sugar before you bottle. His directions are for someone bottling from a keg probably with a beer gun.
Those caps aren’t that important because I think you’re going to be drinking this fairly fresh
If you don’t have CO2 this won’t happen
You can do this with the right amount of sugar
This would be to limit Oxygen, but if you’re bottle conditioning this won’t matter much since the yeast might scavenge some O when consuming the sugar
This happens when you bottle from a keg that is already carbonated