What role did Russia play in the final stages of the First World War?
Russia played very little role in the final stages of World War I. To the extent that it was relevant, it was only in a negative way.
Russia had performed very poorly in WWI. It had suffered many humiliating defeats. These defeats, along with other domestic political factors, led to revolution in early 1917. The Germans had been helping to foment this revolution in some ways as they hoped that it would undermine the Russian war effort. This is, indeed, what happened. The revolution of early 1917 was caused in part by unhappiness with the war and the Bolshevik Revolution in October of that year made change inevitable. The Russians made peace with the Germans, giving up large areas of land in acknowledgement of their defeat. This meant that they played no further part in the war after November of 1917.
The only real impact that the Russians had on the last year of the war was negative. In other words, it was what they did not do that mattered. They were no longer fighting the Germans on the Eastern Front. This freed up large numbers of German soldiers (though not as many as hoped) for service in the west. By doing so, it probably helped to prolong the war to some degree.