If we're talking about modern days in the United States, here is the difference.
Liberals believe that the government should be pretty deeply involved in the economy. They think that the government must do this to prevent unfairness to poorer people and to prevent companies from doing various kinds of bad things (pollution, low wages, etc).
Conservatives believe the government should leave the economy alone (if they are true conservatives). They believe that a free market, left alone, will produce the best effects.
Radicals want the government to run the economy. They want the government to not just regulate things but to actually own all the "means of production." They want all companies to be run by the government.