Across the middle of the MODALapp there are the 12 modulation slots with 8 user configurable and 4 pre-defined options. Only valid modulation destinations for the respective source will be shown in the
drop down menu.
To understand how it works, you need to choose a source that you wish to use such as Velocity or Y+ joystick for example.
Then choose the destination you wish to control with that source.
So once these are chosen you are effectively giving control of the source to another area of the app.
We also have a YouTube video that gives a quick explanation of how to use this feature.