Infinitive Verbs
Infinitive verbs are used in various ways, the most common ones are:
In the Imperative Mood
The 'Imperative Mood' is used to give instructions or commands. When the imperative mood is used, the subject is not included as it is understood to be 'you', the listener or reader. For example, 'Press the on/off button" in a manual. There is no subject included but you, the reader, understands it is yourself.
With the Auxiliary Verb, 'do/does/did'
The infinitive form is used with the auxiliary verb, do, and its various finite forms, in question formations and in emphasis or affirmation. Of course, when a question is formed, 'Inversion' is used, in other words, the subject and finite verb word order is changed.
Do you live here?