Here is the general procedure:
- go through US immigration
- find out which belt your bags are on and get your bags.
- go through US customs.
- look for the Connecting Flights counters(on the left immediately after you exit customs) to drop your bags for your Delta flight.
- follow signs for Airtrain.
- take Airtrain on track 2 to Terminal 3;
- cross over to Terminal 3, go through security and look for gate number for your flight to Toronto.
Here is the general