The function of a transitive verb is to demonstrate the action that the subject is taking on the predicate. For example, in the sentence "Tommy ate an apple", the transitive verb is the word 'ate', and it is showing us what Tommy did to the apple.
There are also intransitive verbs, that demonstrate action being taken by the subject, even when there is no predicate being acted upon. For example, take the sentence "Tommy ran to the store". There is no predicate that the verb 'ran' is acting on, but we still know that Tommy ran somewhere, and the adverbial prepositional phrase 'to the store' tells us where Tommy ran.
Hope that helped! =)
