At some grocery stores in Canada you rent the cart. This is to prevent people from leaving the cart in the parking lot. In order to get a cart you put a dollar coin (known as a Loonie) in the slot near the cart's handle. Once the coin is in the slot the chain will become disconnected so you can take the cart. When you are finished you can connect the cart to the other carts in the designated cart area and take your loonie back. You can see the coin slot in pictures below.