bring to/for

I would say for.

it means john brought a book to mary. the above sentence which you wrote is correct grammatically

Oops, sorry. I was inattentive and thought it was the word "bought". For "brought" there should be "to" indeed.

Bring Helen a present. = Bring a present __ Helen.
Which preposition should I use, for or to?

Bring a present for Helen, in almost all cases.

I suppose, if Helen and Mary were both wrapping the gifts you had bought for the charity, and Helen was ready to wrap another, you COULD mean bring it to her to wrap, but in 99.9% of the cases, it would be understood to mean that the present was intended for Helen.

Which does the above sentence mean? ...

See

John brought Mary a book

can mean either of these:

John brought a book to Mary.
John brought a book for Mary.

The reason is that the verb bring can take either to or for, and the transformation from either of these to a double object constructi

John brought a book to Mary.
John brought a book for Mary.
What's the difference in meaning between the above two sentences?

to Mary means simply that you are carrying it over to her.

for Mary means that it will belong to her afterwards (unless it specifies othewise - but she will keep possession of it for at least a little while).

John brought his daugther Mary to his son's baseball game, but Mary gets easily bored watching sports, so John brought a book for Mary.

Mary saw a big old hairy spi

(1) John brought a book to Mary.

In this sentence, the verb 'bring' is dative, and John brought the book and handed over it to the recipient Mary.

(2) John brought a book for Mary.

Here, the verb 'bring' is benefactive; John brought the book, and he might either give the book to the beneficiary Mary, or change his mind and keep the book wit

Replace the word Mary with 'her' ; it is very clear.

John bought her a book.

John bought her some flowers.

The necessity of 'to' or 'for' doesn't arise.