The outline around a door is called a jamb. The jamb consists of three sides, the head side, the hinge side and the strike side. The strike side is the side opposite to the hinges, where the door handle is.
The video mentioned that no two hinges are the same. Sometimes due to manufacturing defects, some hinges have a better gap when closed compared to others, even from the same manufacturer.
Always start by seeing the big picture, by examining all the gaps of the door. This allows you to have an idea of which hinges to adjust (sometimes it’s both).
A hinge can be adjusted by squeezing or spreading it.
To squeeze a hinge, pop up the pin using a hammer and a nail set or a paint scraper. The pin should only engage with the top two knuckles of the hinge—1 of the leave knuckle and one on the jamb knuckle. Then, use an adjustable crescent wrench to squeeze the two unengaged knuckles connected to the door side away from the hinge jamb. Be extra gentle on the bottomost knuckle as it is the easier one to ply open.
To spread a hinge, push the nail set hard on the hinge barrel and gently close the door to bend open the hinge. Be extra slow and gentle when closing the door, as it can strip out the threads from the screws of the hinge. Do this for two to three sides of the hinge.
Warning
The spreading technique above doesn’t work well for bright brass hinge or soft brass hinges as it’ll leave a big dent.