To qualify for Nationals, couples need to get points - from Russian Cup Series or from Senior or Junior Grand Prix Series. There are five Russian Cup competitions - in Samara's region, Sochi, Yoshar-Ola, Kazan and Moscow. The couples with the highest points will qualify for Nationals - last years there were 9 or 10 couples at Nationals.
For Russian Cup - 1st place means 18 point, 2nd place 16 points etc. I didn't find points for Grand Prix's results.
Junior Ice Dance couples don't compete in Senior Cathegory because it would mean two different SD and practising two different compulsory steps. Stepanova & Bukin tried last year to compete at both junior and senior stage (they had an advantage of having similar style of SD's for both junior and senior dance that year, so they didn't need to change music), but it was not successful either.