Look at the following up script:

CREATE TABLE messages (
  id SERIAL PRIMARY KEY,
  timestamp TIMESTAMP NOT NULL,
  channel_id INTEGER NOT NULL REFERENCES channels,
  user_id INTEGER NOT NULL REFERENCES users,
  text TEXT NOT NULL
);

It creates a table that contains a message that is associated with a channel and a user by ID. Also, it contains a timestamp showing when the messages were added, as well as the text of each message.