If a bearded dragon has is tongue out all the time what does that mean?

It coud mean he is too hot or dehydrated. Reptiles don't sweat like people do, and will try to regulate their temperature by opening their mouth instead.

Check the temperatures in his enclosure with a digital thermometer (the fish tank thermometers are no good, a digital one will cost maybe $20) in three or four places and make sure that there is a spot somewhere where he can cool down. Also give him a lukewarm bath in the tub or the sink and see if he drinks a lot of water.