Have you added the switches for which you want to see the ports already?
And from this statement "i've noticed that i can configure the NPM with this option: interfaces with high precent usage.", i believe you are trying to create a view
Correct me if i m wrong.
There are number of tutorial videos available on youtube as well on thwack. And if u are having access to customer portal then they have virtual classroom vidoes which shows in details about this features.