On the right or left side of either the home page or the lesson is an Rr (only in cyrillic) click that and it should change from English to cyrillic. Sorry not more precise. I'm not signed up for Russian so haven't seen it myself.
Then for typing the answers you add the cyrillic keyboard to your system preferences. On a Mac you can toggle between them by pressing command + 2. There is also a "show keyboard viewer" which is really useful at first.