Questions and negations with main verbs other than BE require use of an auxiliary finite verb. If the finite verb is not an auxiliary or BE, it is replaced by the appropriate form of DO + its infinitive; this is called DO-support.

This tag is for questions about the use of auxiliary DO in questions, negations, and emphatic sentences. Oft-asked questions about Do-support include:

The difference between "She likes cats" and "She does like cats."