John identifies several Passovers that span the length of Christ's ministry, and the first Passover that is identified is the one when Jesus cleanses the temple. Since the synoptic gospels say that this happened on the last week before Jesus' death, this raises the very real possibility that Christ cleansed it more than once.
Jerusalem was packed during the days leading up the Passover, and to avoid having travelers driving livestock through the town, the livestock trade was brought into the outer court, the court of the Gentiles. The business of the Passover had taken over, which was a pragmatic reaction to the logistics of managing the Passover sacrifice. So Jesus drives the merchants out of the temple, fulfilling the prophecy in Psalm 69.
Nicodemus comes to see Jesus, who tells him that he needs to be born again. This confuses Nicodemus, since conversion was not something that he expected.