Who makes the decisions in a Communism country?

Under Communism, there is no state, and thus no central government. As such, there are no leaders, however there may be local committees and councils made up of the local population that make the decisions of their commune.

Its worth noting that communism is different to socialism. Communism has never been achieved (even by so called 'communist' countries), only socialism. under socialism, most decisions are meant to be made by the working class.