But advertisements do not only give information, they also try to influence our emotions.
In this sentence, I'd like to know the usage of "do".
Hello thein lwin
"Do" is a dummy auxiliary verb in your example. It has no meaning of its own - it simply permits compliance with the grammatical requirement that negative clauses should under certain conditions contain an auxiliary verb. Which is why it's referred to as the dummy auxiliary do.
But in sentences with negative + positive coordination (as in your example), where "not only" precedes a lexical (i.e. non-auxiliary) verb like "give", then "do" can be omitted, so we get alternation between the two constructions:
1. But advertisements do not only give information, they also try to influence our emotions.
2. But advertisements not only give information, they also try to influence our emotions.
In ex 1. (yours) syntactically the negation is associated with "do" as opposed to "not only" in ex 2. where "do" has been omitted".