To locate it:
1. Open the hood: Locate the hood release lever (usually inside the car near the steering wheel or under the dash) and open the hood.
2. Look around the engine: The overflow tank is usually near the radiator and often has a cap similar to the radiator cap (but smaller). It might be a bit translucent so you can see the coolant level. Look for a plastic tank with markings indicating minimum and maximum coolant levels.
Important Note: Never remove the radiator cap while the engine is hot. The coolant under pressure can cause severe burns. Only check and fill the overflow reservoir when the engine is completely cool.