If you are unlucky and have a car accident make sure you obtain the licence plate, drivers name and NIF number and the name of the insurance company of the other vehicle.
Complete the blue form which you should carry at all times. This helps to record all relevant information and includes space to draw a picture of the accident.
If you are driving a hire car telephone the hire car company for assistance.
If you need an ambulance call 112.
If the car is not drivable check whether your insurance includes a Roadside Assistance element. If so call that number for a breakdown truck ("Grua") to take your car to the nearest garage or your destination.
At the earliest opportunity call the insurance company or his agent and they will guide you through the claims policy.
There is no specific requirement to inform the Police.
Keep Calm. Do not say too much. Make notes in case you need to defend or mount a legal action.