To expand on what others are saying; you'll clear customs in Canada (in Toronto) when you arrive. Sorry if you get a grumpy agent, they're usually not bad though . . . it won't take long unless you're arriving at 5PM on a Friday or a Sunday, but even then maybe 20 minutes.

On your way home you clear in Toronto as well through something called pre-clearance; a US CBP agent will clear you. Clearance on your way home can be a bit slow depending on the time of day you're leaving; get to the airport at least 2 hours early, more if it's first thing in the morning.

When you get home you'll just walk off the plane like a domestic US flight.