AUX infThe auxiliary verb do is followed by the bare infinitive of another verb. The auxiliary and the other verb together form the verb group.
This pattern is used to add emphasis to a verb in the simple present or the simple past tense, for example because it contrasts with something that has previously been said or implied. It is also used to invite someone politely to do something.
He doesn't say too much, but what he does say enhances the conversation.
Well, as a matter of fact, I did want to talk to you about something.
Do sit down.