The batsman never fails.

(Ask the question ‘how often fails?’ and you get the answer ‘never’.)

They usually go for a walk after dinner.

(Ask the question ‘how often go?’ and you get the answer ‘usually’

Dear student, 

Your friend Param has well described the way in which we get answers of the mentioned questions when we use adverbs.

For instance, 

If we ask the question, 'How often does a batsman fail?'

To this, we can get an answer that 'The batsman never fails.'

Hope this clarified your concept. Same goes the explanation for the next sentence as well.