Ivan was a Muscovite or a citizen of Moscow in an era when the Mongols controlled Moscow and most of Russia. The Mongols were warriors from Central Asia who forced the Russians to pay tribute.
Tribute is a payment for protection.
Ivan proclaimed himself czar and announced that Moscow would no longer pay tribute. The Mongols did not attack and the era of the czars had begun. Peter the Great helped to modernize Russia. Peter traveled throughout Europe disguised as an ordinary traveler. He wanted to learn about the rest of the world.