I have a yellow light on on the dash board - what does it mean?

That is most likely the check engine light. This light is to alert you that the computer has noted a fault in one of the car's systems. Take the car to an autoparts store and have them scan the computer for any codes stored. Most parts stores will do the scan for free. Getting the codes will show what the computer has identified so appropriate corrective action can be taken. Hope this helped and best wishes.