Teaching your dog a word is actually quite simple in concept. The first thing you need to do is teach the behavior. Examples of behaviors include sit, down, come, and stay. There are different ways to teach behaviors. Some behaviors you can lure, while others you can capture. If you're luring, it's recommended to get the dog to understand the hand signal prior to working on teaching the verbal cue. If you're capturing, you'll want to make sure the dog understands the sequence before adding in the verbal cue. The important part with either though is that the dog is getting the motions down, prior to adding in the verbal cue. With luring, once your dog understands the hand signal, you can start saying the verbal cue a couple seconds before giving the hand signal. At first the dog will not respond to the word, as it has no idea what relevance it has to the sequence, but with repetition of doing the sequence, the dog will catch on and do the behavior before you're able to do the hand signal. With capturing, it's important that the dog is doing the behavior reliably before you add in the verbal cue. If you try to add in the verbal cue prior to the dog understanding the sequence you'd like him to do, he'll have no idea what the word means.
Another way that dogs understand words or phrases is due to the order of events in which they're used. A couple examples are, "Wanna go for a walk?" or "Wanna treat?". The way that a dog starts to understand the meaning of these is because the phrases or words are said prior to something happening. Most people say "Wanna go for a walk?" prior to bringing the dog on a walk which serves as a predictor of walks. Dogs are smart enough to catch on to these sequences when they're done correctly.
That is how dogs understand some of the things we say. Dogs don't speak human. Pretty much everything that we say to them they hear as "blah blah blah blah blah." This is why sitting down and having a talk with them about what they did wrong doesn't and will never work. Too bad, right? Wouldn't that be great if we could just ask them nicely not to do something again?
In conclusion, if you'd like to teach your dog how to understand words or phrases, the order of events must happen in a particular order. Repeating the word over and over until the dog guesses right isn't the most efficient way either. I know we have all had a tendency to do that in the past. Stay patient, teach the behavior first, and then add in the word you'd like to use. Thanks for reading.