The most popular food in russia it is borscht. This is a red soup made from beetroot. People eat it with sour cream.
Try blini - these is same of pancakes. You can eat them with meat fish or jam. Also try pirozhki - these are small baked pies with different fillings.
you should go to Stolovaya for traditional Russian food. It is not expensive For fast food try Teremok where you can get blini quickly.
Teremok is very popular for blini and porridge People also like to eat pirozhki from street sellers
you should try syrniki it is sweet cheese pancakes. People eat them with jam. Also try Ptichye Moloko it is a soft, sweet cake.
other food might people want can be in summer kvass it is a cold drink made from bread. . Also try shashlik this is meat cooked over fire.