Rooms with the “free cancellation" label can be cancelled free of charge, if cancelled within the time period specified by the hotel's policy. Most hotels will designate this policy in the room details. This should also be listed in the confirmation email you receive once you've booked.
Rooms with the "non-refundable" label are rooms for which you would not be eligible for a refund in the case of any changes to, of cancellation of, your booking. The policy will provide whether the the booking total, or a cancellation fee, would be charged upon cancellation.
Rooms with the "pay later" label are bookings for which you can pay for your reservation at a later time, rather than at the time the reservation is booked. Typically, this means that customers can pay directly at the hotel upon arrival. Sometimes, however, the policy will specify a date for payment - for example, 1 week prior to arrival. If applicable, this policy will be noted among the room details and conditions.