In the Orient Long Man's dictionary Word Master I have found the different uses of ' to' - as a preposition, to infinitive and an adverb
The example is given for its use as an adverb
He was unconscious for some time, but now he has come to = return to a conscious state.
Native speakers can understand its meaning but non native speakers of English can not understand What "come to" means
What is "come to " here? Is it an idiom or something else?
I would like to know how "to" can be used as an adverb in different contexts?