with a graphic EQ, the parameters (frequency and Q - or bandwidth) are fixed and all you can do is adjust boost or cut at the chosen frequency. Many find the graphic easier to use because the row of sliders is a graphic indication (hence the name) of the curve being applied to the signal.
With a parametric, each of these parameters can be adjusted over a wide range and with some precision, although with digital parametrics, like the Behringer, there is a limit to the resolution of the adjustments, technically, though you will find all the precision you will realistically need. Much more precise adjustments to the signal can be made.
Also, parametrics sometimes include peaking or shelving characteristics to each band for more flexibility.
They are typically installed just before the power amp(s).
Hope this helps.
