To put it simply:
The MIDI Remote translates for your hardware controller. It is its job to receive the messages, and create virtual elements, all these pots and sliders you see.
Then, the Mapping Assistant allow us to connect those virtual elements to functions within the software.
The RCE is the special thingy that allows us to manage and re-order how any plug-in (audio or vst instrument) presents its parameters. Everything you see in a plug-in, almost everything, the cutoff knob, ADSR sliders, whether the strings of the virtual bass are new or old, whether the virtual piano’s tuning is 440 or 442, they’re all Parameters.
Here’s a step-by-step that I had written for another member. It’s not hard once everything comes together.
Edit: This writeup is for Insert Plug-ins. For virtual instruments, we should use the parameters found under “Instrument” in Selected track.