Thanks for your interest in MIR 3D!
From Cubase's point-of-view, MIR basically is "just another plug-in". The main difference is that all instances of this plug-in share a common main GUI window. Each instance is represented there by the so-called MIR Icon that is used to position and rotate the source on the sampled stage of a MIR "Venue", and to control other aspects like its width and its volume. That's about it! 😊
My most important hint: You should stick to stereo tracks in Cubase/Nuendo, as this DAW is not able to change from mono to stereo just by instantiating a plug in. (In case you aim for surround- or 3D-format, there is a nifty little trick that allows for instantiating MIR as a replacement for Cubase's panner that consequently outputs the target format, though.)
There are several feature-specific videos available on MIR 3D's product page. Please find MIR 3D's manuals and additional tutorials here:
-> https://www.vsl.info/en/manuals/mir-pro-3d/introduction
-> https://www.vsl.info/en/tutorials/guides/mir-pro-3d-exploration-pack
-> https://www.vsl.co.at/en/Vienna_Software_Package/MIR_Pro_3D#!Video_Demos
Using the search-term "MIR 3D Pro" on YouTube will bring up more useful videos, too, eg. one that covers MIR 3D's powerful preset management.
... please don't hesitate to ask in case you need more specific info.
Enjoy MIR 3D! :-)