Honestly, "to dinner" and "for dinner" are both grammatically correct, but in this specific case I'd chose "for dinner". Although there are definitely situations where I would chose "to dinner" instead; the difference between them is small but it's there. This website might help: http://ell.stackexchange.com/questions/7973/to-dinner-vs-for-dinner

Both are correct, common, and interchangeable. There's no difference in meaning.

Both are correct, but the version with 'to' suggests a more formal occasion. We might say, for example, 'He took us out to lunch', if this were a formal kind of lunch. But you would say 'We went out for breakfast/brunch/coffee' because these are informal outings. I don't think that we would use 'to' with these nouns. If in doubt, use 'for', as it can be used for any kind of outing of this type, e.g. 'Do you want to go for a drink?', 'Let's go for a pizza after the show' and so on.

Both are correct. But what exactly do you want to know, when you ask each question?

I would like to choose "for dinner" instead of "to dinner" because it's correct and don't know how to described this "why it is correct??? "