Advent: The first season in the Church year. We prepare for the birth of Christ. The priest wears purple.
Christmas: We celebrate that God became one of us to save us. The priest wears white.
Lent: We prepare for Easter. We pray for God's mercy and remember Jesus' life and death. The priest wears purple.
The Three Days or Tridium: The three days that celebrate the passing of Jesus from death to life. They are Holy Thursday, Good Friday and Easter
Holy Thursday: The day of the Last Supper when Jesus first turned bread and wine into His body and blood. The priest wears white.
Good Friday: The day Jesus died. The priest wears red.
Easter: Jesus rose from the dead. We celebrate for 40 days and the priest wears white.
Ordinary time. The longest season of the Church year. It has two parts. One is between Christmas and Lent and the other is after Easter, until Advent. The priest wears green.