"I refer to that."
Translation:Αναφέρομαι σε εκείνο.
There are various ways to get theories etc for each skill. One, of course, is the Tips & notes section on each skill. Then there are various resources which we've added to the Forums https://www.duolingo.com/topic/936.
And of course, there are the mods who are ready and willing to explain whatever we can. Just give us more specific details on what you find confusing and we'll do our best to guide you.
Awaiting your reply.