How do I correctly connect the C3 charger to a battery?

Connect the red (+) terminal of the charger to the (+) terminal of the battery first, then connect the black (–) terminal to the (–) terminal of the battery (or to the car body, well away from fuel pipes). Make sure both terminals are firm before connecting the power cord to the mains. Never connect the power cord to mains current before the terminals are securely attached. (Page 5)