Even though this very, very old Russian film has quite a lot of intertitles for the time, the plot (such as it is) is still pretty difficult to follow if you're unfamiliar with the story, so it's worth familiarising yourself with the tale before watching the film. Much of the film comprises of thirty or so cossack types waving their arms about on a boat on the Volga or in a forest clearing to demonstrate firstly what a grand time they're having, and then how unhappy they are. It seems they are rebels whose leader has gone all soppy over some princess, so they hatch a diabolical plan to win back his leadership. It's all a little confusing, but it is redeemed somewhat by quite a bold and unexpected conclusion.
Review of Stenka Razin
