Who makes the decisions in a socialist country?

It depends on what one sees as a socialist country. Australia is to some extent a socialist country in that it has a mixed economy where the government is involved in the infrastructure and the welfare of its citizens. This is paid for by its Citizen through taxes and various levies. Australians live in states and Territory's, each of these has a separate government that makes decisions on laws and infrastructure that affect the people. the people vote for these governments. then the various representatives that the people voted for make decisions among each other in the same way. If the people are not satisfied with the performance of their representatives they are welcome to vote for a different one at the next election. Australia is a federation of states and on a Federal level the same thing happens. The federal leader is called the Prime minster and The state leader id called the premier.

Whether a country is socialist or not need not make any difference to the democratic leadership of the country.