There are many people who say that dogs do not understand what we say to them and they are right, in part. It is true that dogs are not capable of understanding our language like a human, if by language we mean the language or the words we use. But they are able to understand and identify simple sounds and voice punches (hence they learn words) and, above all, the tone of the voice and the attitude with which it is spoken.
On the opposite side are those who defend that their dogs are capable of understanding complex sentences, such as: why have you bitten my slippers? Who is the most handsome dog in the world? or let's go for a walk! The truth is that your dog does not understand any of these phrases as such, but it is perfectly capable of understand your attitude or goals due to factors such as tone of voice, posture or the number of times you have heard that phrase and the events that followed.
For example, it does not matter what your dog has eaten or if he has peed inside the house; he knows he has done something wrong because he identifies in your body language and in your tone of voice that you are not happy. You probably know these two traits because you have observed them before and you know how to recognize them, you have learned. It is similar to when you take him to the park and another dog, for whatever reason, growls or barks at him. Surely your dog will avoid approaching him to avoid confrontation.
In the same way, if you speak to her in an affectionate tone and encourage her to come closer to you while saying nice things to her, your pet will associate those factors with something good that makes her happy., regardless of the words you are using.
In case you have any doubts about it, the following video is very clarifying. Look how the attitude of these two dogs changes when their human speaks to them angry or affectionate and you will understand how important it is that we learn to communicate with them correctly. Try not to shout or speak to them in a serious tone if they have not done anything wrong and pamper them whenever you can..