Digital Biquad filters
A biquad is simply a two-pole IIR filter, where both the numerator and denominator of the transfer function are quadratic equations.  Thus, you can factor the coefficient equations, and then use any reference regarding a filter's behavior related to pole/zero placements in the Z-plane to determine the behavior.

One tutorial method I recall was a software package where you could drag the poles and zeros around and see a plot of the resulting response.

Q is a term from classic analog filter design which relates the inverse of bandwidth relative to center frequency.  So, given a known center frequency, the use of Q or bandwidth (depending on your exact interpretation or measurement method) is roughly interchangeable (after reciprocating one of them).