Jesus told Peter and John what to do to prepare for Passover. They followed his instructions, and all the disciples gathered for the meal. Jesus took his place at the table then told them, "I wanted to eat this meal with you before I suffer."
We may not be as familiar with Passover as Luke's first readers were. Look back at Exodus 12. God gives instructions to those Jews living in bondage in Egypt. They have just witnessed the series of plagues--frogs, gnats, flies, disease in livestock, skin sores, thunderstorms, invasion of locusts, darkness--but Pharaoh had refused to let them go. God told Moses that because of that refusal. one more plague was coming--the death of the firstborn sons. God then instructed Moses of how the sons of the Jews were to be saved.
Prepare a meal. Serve lamb. When you cut up the lamb meat, put blood on your doorposts and lintels. That night all the firstborn of Egypt will be slain. The blood will be a sign to me to pass over you.
In Jesus' time, centuries after that Exodus, the Jews were again subjected to a foreign ruler, Rome this time, not Egypt. They still celebrate the memory of that first Passover, that time of escape, with a meal.