Socialism and Communism are largely the same (the former is a political & economic system while the latter just an economic system), it can also be said tht Communism is a branch of socialism...anyway both advocate the collective ownership of the means of production and distribution of goods…in socialism many people in government administration have control over the economy while in communism its usually a single-party having authoritarian rule…(yeah it gives TOO MUCH POWER to a small group of people) In both these doctrines, everyone is promised a fair share (atleast theoretically) of goods & services…in communism people get according to their needs (leaving no difference b/w rich and poor, educated & uneducated) while in socialism its according to their deeds/efforts….however production needs to be increased drastically in order to meet everyone’s requirements which to date has not been possible.
Both these are in contrast to CAPITALISM which can be simplified to “survival of the fittest”…here the rich get richer while the poor remain poor (infact that’s where the system leads to eventually, small group of people own most of the money, resources)…it advocates “free market” (that is no regulations, free trade, no duty customs etc, in it prices are determined by demand and supply)…due to which giant corporations and BANKS can monopolize the economy and take exclusive control of nations wealth...(thats whats happening today in US and Eurozone)...As the policies are determined by private individuals, it is more government-free (NOT 100%)...eventually giant corporations get powerful enough to have a say on how the country is run say through lobbying etc. The pros are it can lead to rapid indutrialization, booming economic growth - as the workforce can be exploited by the employer with no checks in place...
Liberalism, as the name suggests tends to remove all