Dashboard Lights

Nowadays cars have different self-check actions which alert the driver in case of malfunction through the dashboard warning lights.
it's important for the driver to know whether a warning light requires immediate attention or whether he can continue his journey and get a garage to investigate later.

If a warning light comes on or doesn't turn off after having started the engine, the driver should stop as soon as possible in a safe place.

Oil Pressure

If the light stays on after starting or illuminates during a journey, stop immediately, switch off the engine and check the engine oil level.
Add the necessary amount of oil if the oil level is low.
If the warning lamp illuminates, even though the oil level is correct, do not start the engine and seek assistance.

Battery charge

If this light doesn't illuminate when you start the engine and switches off or illuminates and doesn't switch off, or if it illuminates while driving, your battery is not being charged.
The reason could be one of the following:

• slack battery or starter terminal
• a broken or loose alternator drive belt
• an alternator failure

If the drive belt is broken, it must be replaced before you restart the engine. The coolant system may rely on this belt and its failure could cause the engine to overheat, in turn causing engine damage. Immediately move the vehicle to a safe location and switch off the engine. Do not restart the engine and seek assistance.

Engine warning light

Illuminates when the ignition is switched on. Should extinguish as soon as the engine starts. If it illuminates with the engine running, it indicates a malfunction with the engine management system. Have this checked as soon as possible.
If it flashes when driving, reduce the vehicle speed immediately until the light illuminates constantly. If it continues to flash, avoid heavy acceleration and high engine speed, stop the vehicle and have it checked immediately.
If it is safe to do so, try stopping the vehicle, switching off the engine, wait two minutes, then restarting the engine to reset the engine management system.

Brake system

This light will remain illuminated when the handbrake is engaged. Illumination after releasing the handbrake may indicate low brake fluid level.
As the brakes wear the fluid level will slowly drop. Check your brake fluid level frequently to ensure there is no further rapid loss of fluid.
If the brake fluid is too low and brake pedal travel is distinctly longer than usual, one of the two hydraulic brake circuits may have failed. Do not continue your journey and seek assistance.
If the light remains illuminated, even though the brake fluid level is correct, this may indicate a sensor fault. Take your vehicle to a dealer or garage as soon as possible.

Diesel Particulate Filter (DPF) partially blocked

Diesel Particulate filters (DPF) catch bits of soot in the exhaust.
They have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration' – the accumulated soot is burnt off at high temperature to leave only a tiny ash residue. Regeneration may be either passive or active.
Passive regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. 
If the journey's a bit stop/start the regeneration may not complete and the warning light will illuminate to show that the DPF is partially blocked.
It should be possible to start a complete regeneration and clear the warning light by driving for 10 minutes or so at speeds greater than 40mph.

ABS warning light
When the ignition is switched on, the light illuminates briefly to confirm that the system is operational.
If it illuminates when driving, it indicates a malfunction. Have this checked as soon as possible.

Brake system and ABS warning lights

If both warning lights illuminate at the same time when driving, stop the vehicle as soon as it is safe to do so.
Reduce vehicle speed gradually and immediately move the vehicle to a safe location. Use the brakes with great care. Do not step on the brake pedal abruptly. Seek assistance.

Fuel filter water trap (diesel engines)

This light illuminates when the ignition is switched on and should extinguish after a few seconds.
If it illuminates while driving, it indicates that water has been detected in the fuel filter.
This light warns you that the amount of accumulated water in the fuel filter has reached the specified level.
Normally the vehicle is quite safe to drive, but have the accumulated water in the fuel filter drained off as soon as possible.
If the vehicle has just been re-fueled, immediately move the vehicle to a safe location and switch off the engine. The fuel may have been contaminated and could cause damage to the injection system.

source: http://www.theaa.com/motoring_advice/breakdown_advice/warning_lights.html