The Last Supper was Jesus' last meal before he died, and he shared two signs with his followers: bread and wine to symbolise his body and his blood. He commanded those who follow him to share this meal together in order to remember him and his death on the cross. That commemoration takes place today in the context of holy communion.
On weekdays, a simple said service takes place on Tuesday to Friday at 12.30pm, usually in the Lady Chapel (at the far east end of the Cathedral).