Communism follows the ideology of Karl Marx. It is a way of leading a country completely opposing the capitalist view of private ownership and free market. In Communism, the State owns everything and controls markets strictly. Marx had the idea that after implementing the ideology, the State and social classes would "wither away". These are reasons why Communism is so hated by Capitalists; it is the end of free ownership and upper-class rule.
An important tool in achieving these goals is nationalisation of foreign enterprise. Self-sufficiency, which is another aim of Communism, is achieved by limiting foreign trade and foreign intervention. The only way to make a country profitable by itself is to train experts and industrialise the country.
Stalin was one of the first Communist leaders, and followed Marx's ideas quite closely. When the Communists took over in Russia in 1917, the country was very backward and inefficient. Stalin ordered collectivisation of everything from farm tools to cattle, and everything was shared amongst the people and brought under state rule.
He sent experts to study abroad and organised education for the people. He introduced the Five-Year-Plans, which were supposed to make Russia a wealthy, industrialised country in just a few years. But, lacking realistic planning, this failed miserably and as people started lying about the results to try and keep up with his mad goals. Factories were built and for some time, Russia really seemed to be making process after the many years under Tsars who weren't willing to do anything about the situation.
When he was finished with planning the industrialisation process, Stalin turned his focus on another key concept of Communism; destroying opposition and establishing a single-party-state. Although all other parties had been banned after the October Revolution, where the Communists took power from the Provisional Government,