Checking the state of the car's coolant must be performed with the car on level ground and with the engine cold.
Check that the level of the liquid contained in the tray is between the minimum and maximum marks.
If the level is lower, top up the level with normal tap water if you do not have the specific liquid that contains antifreeze available.
To do this, pour the water directly into the tray.
The coolant in case of replacement (every 3 or 4 years) must be replaced with what is called "permanent liquid".
This special liquid contains various additives: antifreeze, anti-corrosion, anti-rust, anti-limescale that protect the engine and the other components of the system.