I don't really understand the Instant Process portion of that website either. Don't see what it is telling you to do that would make anything faster.
Basically, check the box at the bottom of the spectrogram that says "Instant Process". From the dropdown menu to the right, you can select things like attenuate, declick, etc. Then, when you highlight a selection with whatever editing tool you want to apply, RX will perform that action immediately.
So for example, Let's say you are going to use the paintbrush tool and your work flow process might be to highlight a scream then click "Render" in the Spectral Repair window that you have open. That's alot of mousing back and forth if you're doing it over and over again. With Instant Process, you would paint over the scream and it would attenuate immediately. So instead of back and forth with selecting and rendering, you simply highlight, highlight the next one, the next etc.