The MIXER is meant to combine signals – it has 3 sections of 3 inputs to mix into 1 output each. By combining a slow LFO triangle signal with for instance a faster square wave LFO signal you can create nice pitch modulation effects for a VCO. Each section has a 3-way switch, that can change the MODE of mixing. Standard mode is +. In this case the signals are added. Next mode is *.
Here signals are amplified. You can use this to create Ring Modulation by sending separate VCO signals to two inputs – use this to create bell sounds. An other idea is to use an LFO medium fast triangle wave on one channel and use the Modulation Wheel signal on the other input. This way the wheel decides how much ‘vibrato’ you can send to the PM connection of a VCO.
Last mode is %. This is a mathematical function that only takes a signal in certain cases. This can lead to unpredictable signals when combining LFOs and Envelopes. You could even create whole new sounds when using VCOs as input and then send the output into a VCF.