It is best to use rewards, so called treats, i.e. pieces of dog treat (e.g. from the company Alfa Spirit) or even balls of dog food, to teach commands such as sit, stay, etc. We start learning by repeating the command loudly, e.g. "Sit!" and at the same time manually moving the dog to the given position. When the dog sits or stands (no matter if on its own or with our help) we praise it loudly and show great enthusiasm while giving it a reward - a treat. Repeat it until it succeeds.
Black terriers learn commands very quickly, sometimes it is enough to repeat a command several times to teach it to a dog.