We're only allowed to answer one question at a time here on eNotes so I've edited your many questions down to this one.
The Russian Revolution in 1917 overthrew a monarchy. Tsar Nicholas II was an absolute monarch, one who kept essentially all power for himself. (The word "Tsar" or "Czar" comes from the word "Caesar.") Because the Russian monarchy had been so oppressive, people rebelled against it in 1917.
After the Tsar was deposed, the rebels set up a provisional government until they could figure out what came next. This was in March of 1917. In October, the Bolsheviks, a communist group led by Vladimir Lenin, started another revolution. After this "Bolshevik Revolution," the communists came to power and set up a communist dictatorship.