To know what warning light it is, you'll need to:
* Describe the light: Is it a symbol (like an engine, a battery, a brake pad, etc.)? What color is it (red, yellow/amber, etc.)?
* Consult your owner's manual: This is the best resource for identifying warning lights specific to your vehicle's year and model. The manual will have a diagram of the dashboard lights and their meanings.
Without more information, it's impossible to say what the light means.