John's gospel takes the baptism of Jesus by John the Baptist at length, because John the Evangelist was a disciple of John the Baptist, and then discusses several signs. A sign is something that signifies something else, in this case, pointing to the spiritual reality that we might not otherwise notice.
The first sign is the Wedding Feast at Cana. The wine runs out at a wedding feast, and Mary (never called by name in John's gospel) asks him to do something. Jesus asks what the situation had to do with Jesus and Mary, but still changes water into wine, signifying the importance of a wedding and thus blessing the ceremony. Doing this, we know that he is able to change reality. He can alter reality and he isn't just changing perception.