Hello Camilo it depends on the sentence. It can be different things.Do you have a sentence? THen I can explain it better.

'Do' is a verb in it's own right which can often have a meaning similar to 'make' as in 'I do my homework every night'. But it can also be used as an auxiliary or 'helping' verb verb in the present and past simple tenses. It is used when making negatives and questions. 'I don't do my homework every night' 'Do you do your homework every night?' Hope this helps Bob

Are you talking about the verb 'to do' or is DO an acronym you don't know? e.g. "Doctor of Osteopathy"