Right what you need to do is make sure the right reed goes in the right pipe, then it helps if you gently lift up the flap of the reed a bit to allow for better air flow, then put the whole of your mouth over the two reeds so that your lips are touching the next section, fill your cheeks up with air and gently blow at first, sometimes its easier to try it with one reed first,

reasons for not getting a sound would be , the reeds are closed so you would need to open them, your lips might be touching the reeds restricting airflow or you are blowing too hard or soft.