at the bottom of the explorer display, you can vizualize all your inputs/outputs. Drag and drop the mic input on your player and hit the record button. Make sure you use a skin which displays a "rec" option. that should do the trick.
BTW Unless you looking to record samples to scratch them or send them in your sampler in MixVibes on the fly. I would recommend using an external software dedicated to recording audio -not that MV won't do the job great, but the interface is not dedivctaed to this kinda job- Pick up goldwave. it's free and great to make samples, that you can then use in MixVibes
