The 1996 Honda Civic doesn't have a readily accessible, manually operated emergency fuel shut-off switch like some other vehicles. The fuel system relies on other safety mechanisms to prevent fuel leaks in a crash, primarily the inertia switch. This switch is located under the dashboard, usually near the passenger side. It's designed to cut off fuel supply in a collision.
There's no easily accessible external switch to manually cut off fuel flow. In the event of a fire, your best course of action is to evacuate the vehicle and call emergency services.