most multi effects will have a few "types" and you can run one of each type at the same time. I think in the Zoom, you have amp, pitch/synth, modulation, OD, compression, EQ, reverb
You can use one of each at the same time. So, you could have octave, chorus, compression, but you couldn't have wah chorus compression, 'cos the wah is in the same "type" as chorus.
I'm not sure about the specifics of each "type" though