Analise, as previously noted, you catch the #192 bus at the airport. I'm not sure what terminal you're arriving at, but the but stops at the "Ground Level" of Terminal 1 (column R4), the arrivals level at Terminal 2, and the departures level at Terminal 3. Get on the front door and deposit your coins (or your $5 bill for two) in the fare box. No need for a transfer.

The bus may stop at other terminals (depending where you get on) and will then hit the highway for the short trip to Kipling Station (~10 minutes). Since Kipling is the last station on the line, you can take the next train that comes in on either side of the platform. (It will say "Kennedy".)

The trip to St. George will take about 20 - 25 minutes. When you get to St. George, follow the signs for "Young-University-Spadina" line southbound. You want to be on the platform that says "To Finch via Union" or something; there's only one train southbound and it should say "Finch".