Notice the extra stress placed on the auxiliaries to clarify or strengthen a point. The underlined word indicates extra stress.

1. a. You don’t understand me.
   b. I do understand you.
2. a. You didn’t go, did you?
   b. I did go.
3. a. It’s hot isn’t it?
   b. It is hot.
4. a. You’ve never been here, have you?
   b. I have been here.