The two emphatic tenses receive their name because they are used for emphasis. More commonly, however, they are used with the negative not and with questions when the normal order is inverted and part of the verb comes before the subject.
The present emphatic tense is formed by adding the basic present form of the verb to the present tense of the verb to do (do or does).
The past emphatic tense is formed by adding the basic present form of the verb to the past tense of the verb to do (did).
Present emphatic: Does he run fast?
He does run fast.
He does not run slowly.
Past emphatic: He did come to work today.
Didn't he stay home?
He did not stay home today.