The TTC buses leave from both Toronto airport terminals. Explicitly, they depart from the Ground level of Toronto airport terminal 1 (Column R4) and the Arrivals level of T3 (Columns C8-C12). You can buy your bus fare onboard (yet only if you have the exact amount of money) or purchase a PRESTO Ticket from the airport's automatic vendors, or opt for a rechargeable PRESTO Card. PRESTO Tickets and Cards must be tapped once entering the bus.