How the iron curtain start?

Answer 1

First, there's an intrinsic problem in your question. You should be asking How DID the Iron Curtain start? or even better, How was the Iron Curtain established.

BUT, assuming your question was as such, the Iron Curtain is in regards to the sphere of influence that the Soviet Union had over the countries of Eastern Europe. These countries, were essentially communist buffer states between the Soviets and the West. It stretched through Germany (divided into two countries) all the way down the map. It was NOT an actual curtain or wall (though it did appear as such in some places), but rather a blockade from within which the Western Nations received little information or communication. Immigration to the West was discouraged by the Soviets.

As to how it "started" it was a result of communist fears of capitalism and democracy. The Soviet Union was (often justifiably) threatened by the anti-communist fervor in the West, and it locked down its borders both as a way to cope with its domestic problems and to protect itself from foreign nations.