First, it should be recognized that there are different definitions for these terms, especially liberalism and socialism. This answer will address the terms as they are popularly used.
Socialism describes a political and economic system where the people, through their government, control the means of production, i.e. manufacturing and agriculture. Socialist systems are generally "planned" economies, in that the economy is regulated and controlled, to a large extent, by the central government. Under these conditions, government generally controls and offers many major services controlled by the private sector in other economies. These include (especially) health care, transportation, and social security provisions. Unlike conservatism and liberalism, the definition of socialism is limited to political economy.
Liberalism historically referred to a general absence of governmental intervention in the economy, combined with a belief in basic human liberties. Its modern meaning, however, especially in the United States, connotes an acceptance of a certain role for government in bringing about social justice, regulating the economy, and providing services. Modern liberals, however, generally reject the concept of government ownership of industries, and support only limited government intervention in the economy. Liberals often define themselves as "progressives" in that they emphasize issues of social justice and civil rights, often advocating positive state action to bring them about.
Modern conservatives generally argue for a limited role for government, especially (in an American context) the federal government. They support the free market, arguing that market forces are more effective in regulating the economy than planners. They often argue against regulations as well, claiming that they tend to have negative economic consequences. Socially, conservatives tend to favor what they describe as "traditional" values, even when these collide with more modern sensibilities. Even those conservatives who favor more progressive values often harbor skepticism about the ability of government to bring about change.