Our heater won't light

we've recently moved into a new house and the previous owners haven't left the instruction manual. we're not sure whether it's broken or we simply aren't doing it right. when we turn the ignition knob around and then press it down we hear the clicking sound that means it's trying to ignite the pilot light but it doesn't light it. we've tried everything we can think of but nothing works. please help- it's very cold without it