What is the grammer error in this : it is very important to train your dog. it keeps your dog’s mind active, and it to build an understanding between you and your dog. often owners will shout at their dogs or even punish them when what is needed is effective training

The important thing to watch out for grammatical error, among others, is the use of the subject-verb agreement. A singular subject must use a singular verb. A plural subject must use a plural verb. Let's investigate each sentence.

"It is very important to train your dog": 'It' and 'is' are singular. Correct.

"It keeps your dog’s mind active, and it help to build an understanding between you and your dog.": 'It' is singular and the verb 'keeps' is also singular. That is correct. But the other clause of the sentence must have a mistake. It should be 'it helps', not 'it help'.

"Often owners will shout at their dogs or even punish them when what is needed is effective training": 'Owners' is plural so it is correct to pair it with 'shout' and 'punish'.