This is the 10606th most frequent Russian word.
водителю
"To the driver" (dative case of "водитель").
In this sentence, "водителю" is in the dative case, indicating the indirect object of the verb "помог" (helped).
Я помог водителю найти дорогу.
I helped the driver to find the road.
Here, "водителю" is also in the dative case, used in impersonal construction to express for whom it is important.
Водителю важно быть внимательным на дороге.
It is important for the driver to be attentive on the road.
Similarly, "водителю" is in the dative case, representing to whom the gift is purchased.