How do I connect a 60 amp dual breaker to a heater

If it is an DEmand type water heater, you should have 4 connections for power, 1 for ground.

Please provide more detail, difficult to answer a vague question such as "how to wire something".

We have no idea if this is a home, a garage, a shed, a pool, a store, or an industrial plant.

You need to come to us with what you have, what type of wiring method, and what you do know how to do.