Now when he was in Jerusalem at the Passover, during the feast, many believed in his name, observing his signs which he did.
Now, John was, by physical birth, a cousin to Jesus. However, John was born before Jesus was born. Probably in about the sixth month of Mary's pregnancy when John was born. Yet, John is saying of Him, "He is preferred before me: for He was before me." So, he is talking about that pre-existence of Jesus prior to His incarnation.