It's plain to a Russian (6)
I believe the answer is:
steppe
'it's plain' is the definition.
(steppe is a kind of plain)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for steppe that I've seen before include "Dry plain of Eurasia" , "Large area of flat grassland in Europe or Siberia" , "(Russian) grassy plain" , "Dry grassy plain of central Europe" , "plain territory" .)