Cybertronians would send messages to one another using their computer systems. Most are encrypted or secret.
Starscream sent Ratchet a message telling him that he had information regarding Optimus Prime's whereabouts and to come alone with medical supplies. Ratchet did but brought Bulkhead along since they couldn't trust him.
Dreadwing sent a message to the Autobots. Ratchet received it and informed the others that Dreadwing wants to meet with them.