Check while the engine idles. FIll to the correct level with Dexron II or III.
If the level was way low (more than 2 quarts), you may have roasted the transmission.

Either way, you should change the fluid and filter, basically to see how it looks at this point, and that's about the only thing we mortals can do. If you have clutch pieces and other debris in there, it's rebuild time. If it looks fairly clean, then it may be repairable, but you should find a tranny shop to look at it.