1. Make sure your Jamstik is powered on and connected to your computer.
2. In Cubase, navigate to Studio->Studio Setup... from the top bar.
3. In Studio Setup, make sure that your Jamstik is in the list, and that both checkmarks are checked on the Jamstik port (you should not have MIDIIN2 or Jamstik Config IN ports selected).
4. If you have installed the Jamstik Creator VST3, select it from the VST instruments section in the media tab on the right of the screen and place it onto an empty instrument track in your project.
5. Select the track with the Jamstik Creator and head to the inspector on the left panel of Cubase. Expand the Jamstik Creator dropdown and make sure All MIDI Inputs or Jamstik is selected in the input section. If you are using the Jamstik Creator or another MPE synth, make sure Any is selected in the MIDI Channel section (default will be set to 1 and flatten your MIDI channels making input only appear on one string in the Jamstik Creator).
6. To view the UI for the Creator inside of Cubase, click on the "Edit Instrument" button with the right-facing arrow in the Inspector. The Jamstik should appear in the Device Settings of Cubase and you can open Device Settings and made sure that your Jamstik and the Creator are set to MPE mode. Make sure your instrument track has "Record Enable" selected. That's it, you can now record with your Jamstik and Jamstik Creator in Cubase!
Make sure to check the Jamstik Creator: Third-Party DAW Compatibility Database for the current state of plugin compatibility with your DAW.