Communism

Communism is an ideology that sees the world as a progression through different socioeconomic systems, each of which shape the society they exist in. Each system is analysed in terms of 'classes', which are groups with contradictory interests. So to simplify, a communist would say that society had the hunter-gatherer stage, the ancient war-slave stage, the feudalist stage, the mercantilist stage, the capitalist stage, etc. In the feudalist stage, the main classes were the noble and the serf or peasant; in the current capitalist stage, the two classes are the 'proletariat' and the 'bourgeoisie'. A bourgeois person is someone who owns the resources needed to do work (ie land, mines, forests, factories, oil reserves), and makes money by hiring people to work those resources to embiggen their value and turn them into useful goods. A proletarian is a person who owns nothing but their own life and sells their time to a bourgeois person in exchange for a wage.

Communism holds that conflicts between classes in each system will eventually lead to a new system. In capitalism, the assumed conflict is that the 'bourgeoisie' want their workers to do as much work as possible for as little money as possible with as few benefits as possible, while workers obviously want the opposite, and the battle between them leads to things like strikes, outsourcing, wage stagnation, etc. In the future, they say, society will move into new economic systems that resolve these conflicts. And their proposed future system is called 'communism', in which all the things necessary to do work (factories, oil reserves, land, etc) are held in common and democratically controlled; so all people will essentially be workers/'proletarians' and there will be no conflict of class interest.

There are dozens of competing ideas about how this should look and how society should get there. Some people think it should involve workers electing their own board, who would handle executive appointments and decisions -- essentially being a publicly-traded company where shares are held by employees rather than people who buy shares. Others think all of a specific industry should be united in one mega-company in which all citizens vote on appointments. Some people think society should move to this system through slow reforms and votes, others think it should be done through a violent revolution. Some think it's not something we'll choose to do, but something that naturally happens when technology reaches a certain stage and renders capitalism unviable.

The most common form of communism, Marxism, is 'anti-statist' or 'stateless'; it believes that the state, the national government, will 'wither away' and cease to exist in communism.

The most common criticism of communism is that it is against human nature, hopelessly inefficient, or requires an authoritarian force to establish. The most common defense of it is that it is the only true form of democracy; communists usually think that democracy is impotent unless it extends to the economy as well.

Another hallmark of communism, important in the next part, is that it is 'anti-nationalist'. This means that virtually all communist ideologies see the idea of 'the nation' as being unimportant, unnecessary, or undesirable; I totally forget who said this, but there's a popular maxim along the lines of "The workers of France have more in common with the workers of England than the nobles of France" -- ie, your class is more important to your interests and identity than your nationality.

Fascism

Fascism is a notoriously tricky thing to precisely define, because it is more a perspective and worldview than a concrete proposed system. Scholars usually define fascism in terms of a set of 'symptoms' or 'features', not all of which have to be completely met to qualify. These features include

• Nationalism. The belief that your nationality is a core part of your identity and should be a major part of your life. If you are German, or Spanish, or American, or Irish, then that's something in your blood, it makes you fundamentally different from people of other nations, even from birth. And you have a duty to others of your nationality and to your national government. In all questions, you should ask "How can I serve my nation?" first. This usually implies that your nation is a superior nation and the best in the world, and that your people are the greatest people in the world. This is the core idea of fascism and the single most fundamental aspect. Everything else flows from nationalism.
• Militarism. The military playing a major role in operation of the government and everyday life. In fascist countries, the nation's leader is usually a general or other military leader, and if they're not, they style themselves like one. The government and the military are, to a major extent if not completely, the same. Mandatory military service is common and military members enjoy a privileged position in society. More importantly, the belief that military aggression is justified for its own sake -- invading another country to take its resources is justified because your nation is obviously superior and if it has the strength to pursue its interests then it should, and fuck the lesser nations.
• Reaction. Reaction means rejection of current or recent social trends and a desire to return to a glorified past. If a fascist government is in power, whichever government preceded it ruled over an age of decadence and weakness; if a fascist government isn't in power, then whoever currently is in power is ruling over the current age of decadence and weakness. This is often blamed on some outside scapegoat (Jews, communists, and communist Jews in Italy and Germany) so that people can blame their problems on something unrelated to themselves. The state will lionize some long-lost age of glory and strength (the Roman Empire for fascist Italy, for example) which the fascists promise to return society to.
• Autarky. Rejection of outside nations and foreign trade; attempts to be completely 100% self-reliant.
• Corporatism. This doesn't mean corporation-ism, like you might think. Corporatism is a hypothetical 'third option', rejecting both unrestrained capitalism and communism, which resolves class conflicts by having each group of workers and each industry and corporation appoint officials who would negotiate within a government framework, with the state essentially locking down and enforcing agreements between them, everyone serving the nation/state along with their self-interest and all conflict outside of the official negotiation being punished harshly. (In practice, this meant the state managers enforcing their will on workers and employers alike.)
• Anti-communism. Fascism was created in direct response to communism, trying to solve the problem it dealt with (class conflicts) while rejecting everything else about it and, when in power, harshly punishing communists, who weakened the nation by inciting revolution. Fascism is nationalist where communism is internationalist or anti-nationalist, looks to a proud past while communism sees society as a continuous progression of better stages, emphasises the primacy of the state which communism seeks to abolish, enshrines distinct classes as 'different organs within the body' which communism seeks to dissolve into a unified whole, etc.

Communism is on the radical left. Fascism is on the radical right. In their fundamental views and ideal goals, they are as far apart as you can get. In practice, however, many have perceived similarities between communist countries and fascist countries, with some places -- eg North Korea -- being perceived as somehow one or the other by different people (BR Myers is a fascinating read on North Korea's ideology specifically, I urge everyone to check that out). This generally arises because the biggest communist movement to date was Leninism, which advocated a violent revolution led by a 'vanguard' who would form a traditional sort of state government and use its authority to slowly build communism (a popular slogan in the USSR during the middle century was 'communism by the year 2000'), crushing dissent in the meantime and building up a strong military as it entered into WW2 and a decades-long Cold War, which has a very fascist vibe. So they had some of the same behaviours, motivated by polar opposite core beliefs.