From Helping and Modal Auxiliary Verbs
Emphatic do has many uses in English.
To add emphasis to an entire sentence: "He does like spinach. He really does!"
To add emphasis to an imperative: "Do come in." (actually softens the command)
To add emphasis to a frequency adverb: "He never did understand his father." "She always does manage to hurt her mother's feelings."
To contradict a negative statement: "You didn't do your homework, did you?" "Oh, but I did finish it."
To ask a clarifying question about a previous negative statement: "Ridwell didn't take the tools." "Then who did take the tools?"
To indicate a strong concession: "Although the Clintons denied any wrong-doing, they did return some of the gifts."
In the absence of other modal auxiliaries, a form of do is used in question and negative constructions known as the get passive:
Did Rinaldo get selected by the committee?
The audience didn't get riled up by the politician.
Try here also: Kibbitzer 42. Emphatic 'do'.. It says, "The Emphatic Do quite often causes difficulties for learners of English. Those difficulties can best be avoided by thinking of it as having a contrastive meaning, as shown by the following citations."
And here too:Modals and auxiliary verbs in English. Go to Auxiliary do, Range of forms, Nonfinite contexts, and Do support contexts.