If you spot a tornado on the ground, first and foremost take shelter!  As important as your report is, it is critical to protect yourself fist.  Once it is safe to do so, relay your report to the NWS as soon as possible.  Many times cloud features look like tornadoes, so be descriptive (but not too wordy) when you report a tornado.  Is a funnel cloud clearly touching the ground?  Do you see debris?  Is your view obstructed?  Is the funnel cloud visibly rotating?  If you're not confident you see a tornado, that's ok!  We want to hear from you anyway.  Just be sure to convey you aren't confident it's a tornado, and describe what you see.  If you are confident, be sure to say so.