You put an appropriately-sized capacitor in parallel with the feedback path of an opamp, with a series resistor for a shelf:
I think the C2 - C3 values might be reversed there, but it's early and I'm tired and not thinking too clearly . . . It's from this site though, I didn't draw it:
Either would work. There are plenty of free synth VST plug-ins that would be good to learn on. Im sure someone on here could suggest a good simply and free VST synth, if your DAW supports VSTi's that is.