One day, John was doing whatever he was doing when priests and Levites asked who John was. Take note of the responses:
John is not the Christ (1:20). Jesus is. John didn't die on a cross!
John is not Elijah (1:21). Elijah is a historical figure.
John is not the Prophet (1:22). The Prophet with a capital P is likely referring to one of the prophets that Moses talked about way back in Deuteronomy 18:15. In fact, at that time, John did not reveal anything new aside from his preparations, and Jesus was the one who reveals new stuff about God.
So who was John? As said from the words of Isaiah (another prophet), John says that he is the "voice" who proclaims to "make straight the way of the Lord" (1:23). That sounds a lot like a messenger!
A messenger's job is to relay information, and that role sounds like what John is trying to do. Later on, in a sense, we are all messengers. Jesus is the one who does all sorts of incredible stuff within us and through us. Pretty much all that we really do is receive it, trust in Him who does it, or relay it.