Purchase an Opus card for $3.50 Canadian, as of 2008, at a location that sells them. Locations include the subway station booths and pharmacies.
Insert the Opus card into the reader.
Press the button indicating the type of purchase you want to make (monthly pass, CAM Hebdo, six tickets, single ticket).
Press the button indicating the type of payment you will make.
Insert payment of coins, bills, credit card or debit card.
Wait until the card is charged and remove it.