You can play the TrueGrid synthesizer with your MIDI keyboard, just as you do with other softsynth plugins.
However, MIDI needs to be supported by the browser and at this time it will only work in Google Chrome.
Here is how you enable it:
If you hear no sound check this:
If you want to configure your own synth just drop the Pittsburgh Midi module to your custom rack.
For classic functionality you should connect the MIDI modules CV output to an oscillator 1V input and the gate output to an envelope gate input.
But since it's a modular synth you can patch as you please.