Here are a couple of basic charts on tongue diagnosis.
In theory you could link channels to the organs and their respective areas of the tongue. But I've generally found the tongue to be more indicative of organ, vice channel, dysfunction.
The tongue is normally one of two main diagnostics used. The other being pulse. Some other less often used systems include face reading , eye reading, abdominal palpation and palpating the channels in the extremities to name just a few.
Pulse and tongue are consulted together to come up with a comprehensive diagnosis.
Generally speaking, the pulse changes faster than the tongue. Both can fool you depending upon what drugs the person is taking (prescription, OTC and illegal).
A tongue coating is usually an indication of some kind of phlegm in the system as well.
Without a lot of training, try not to read too much into this. Reading the tongue and pulse are arts unto themselves.