Please explain the government structure of the Soviet Union.

During the time that the Soviet Union existed, there was
an official structure of government and an unofficial structure which held the true
power.  In essence, the Communist Party was the true government of the Soviet Union,
regardless of what their constitution said.

Under the
Soviet constitution, there was a legislative branch, an executive branch, and a judicial
branch.  The Supreme Soviet was the legislative branch and it was officially in charge
of making laws.  The Chairman of the Praesidium of the Soviet Union was the official
head of state and head of the executive branch.

However,
the real power in the Soviet Union rested with the Communist Party.  The true ruler of
the country was the General Secretary of the Communist Party.  This was the post held,
for example, by Stalin who had no official governmental post.  It was the Party that
dictated policy and had the true power over what was done in the Soviet
Union.