lol... It seems I'm lacking some requisite knowledge

I started watching a vid about this 

and dude was like

"Tritone substitution is... a Jazz chord substitution theory"

I don't know anything about jazz

and then he said I need some understanding of 

Functioning Dominant

Altered scale

Altered harmony

"...or this probably won't make any sense at all."

I was like
"ah I'll just watch while I eat dinner anyway"

nope. dude is right... I'm completely lost.