"What is the difference between communism and socialism?"
A lot of people as socialists this question, mainly because they themselves don't really know what the first one is, much less the second.
Socialism is the idea that the working class, the class that produces the profits, the wealth, the cars, houses, planes, steel, should take over and run things collectively, democratically, for the benefit of the majority (who also "just happen" to be workers too).
Communism is the idea that society should not have classes - exploiters and exploited, oppressors and oppressed, and so on.
The difference between the two? There isn't one; they are both stages of the same thing. If the working class takes over and runs society for human need, and the capitalists' resistance is crushed and they get hungry and have to get jobs like everyone else, then we have a society without class divisions, or a classless society.
Today we live in a capitalist society - with gross class inequalities. If we want a society where everyone is truly equal (communism), we cannot get there overnight. Socialism is the bridge between capitalism and communism; it is a transitional period that has features of both the society of yesterday (capitalism) and tomorrow (communism) because it will inherit the world capitalism has left it.
Instead of people and money going into something like, say advertising, we could use those skills and talents and money in schools, or in health care. Nuclear arsenals will have to be dismantled, the steel and concrete used to build things that we need, like housing for the homeless.
While production will be for human need, there will be some need for a state apparatus to ensure that the capitalists don't come back and restore their rule. But eventually, if the capitalists are overthrown in country after country, they will have no haven in which to hide and plot; they will get tired and hungry, and have to come back and get jobs in the factories with the rest of society.
When everyone has the same relationship to the means of production - when every member of society has direct control over his or her workplace - then we will have communism.