I'm not sure what resources there are these days, but I'm pretty sure that one of the online training videos covers calculations pretty well.
In terms of your example, what you want is:
( [Current Weight] / SQUARE([Height])) * 703
EXP(2) is actually returning you the mathematical constant e (Euler's number) to the power of 2, so your expression:
(EXP(2) = [Height])
is actually testing to see if [Height] = e^2 - which was not what you wanted at all!
If you click on a function name in the calculated field editor you will get a brief description of the function:
Hope that helps.