Trouble assigning second extruder to material (dual color or use second extruder exclusively)

[dcbarry]

I;ve seen the Multi-color support page ( https://www.matterhackers.com/mattercontrol/support/printing/multi-color-stls?search=multi )

But, I'm still unclear, how do I assign a given extruder to a material. That doesn't seem to be explained. And the only other extruder number reference I see is to assigning a "support material extruder".

While on the topic, how can I simply assign a mono-color print to print from extruder number #2?

Sorry, I promise I have read the FAQs and support guides.