The Russian Empire was a historical empire that extended across Eurasia and North America from 1721, following the end of the Great Northern War, until the Republic was proclaimed by the Provisional Government that took power after the February Revolution of 1917.
Tsarist Russia: This refers to Russia under the rule of Tsars or emperors. It's like being under one strict principal who makes all decisions for your school.
Serfdom in Russia: This is similar to slavery where peasants were tied to land owned by nobles. Imagine if you had no choice but to work at your school cafeteria without pay because your parents did it before you.
February Revolution: A series of protests in Petrograd (now St. Petersburg) that led to abdication of Tsar Nicholas II and establishment of a provisional government. It's like students staging a successful protest against unfair rules leading to change in school administration.