When a Tornado WATCH is issued by the weather service, you are advised to take precautions. A tornado watch means that conditions are favorable for a severe thunderstorm or a tornado to occur.
When a Tornado WARNING has been issued by the weather service, you are advised to take action, immediately! A tornado warning means that a tornado has been sighted or indicated by local weather radar. There is imminent danger to life and property.
More about Tornado Advice.