Fascism is a hard ideology to define because nearly every modern government or political movement has been called 'fascist' by somebody. I contend that fascism was a political movement unique to the early 20th century, especially in Europe, because its worldview was shaped by events and philosophical ideas from the late 19th century until the interwar period. Some people have called states like Saddam Hussein's Iraq 'fascist', but I believe that there is a big difference between authoritarian dictatorship and genuine fascism.
So how did fascism originally develop? It grew out of a European intellectual movement which criticized the alienating effect that industrial society had on modern man, as well as late 19th century critiques of Liberalism and Positivism. They believed that industrial society robbed men of their individuality; however they wanted to assert it at the same time. These ideas were adopted by many young people, especially young, middle-class socialists, because they wanted to rebel against what they perceived as pointless and archaic bourgeois morality and conformity. This is why in the 1930s, fascism looked like it might actually take over Europe: it successfully harnessed people’s dissatisfaction with modern society and directed it into political channels.
Fascists were influenced by philosophers like Gustav Le Bon who wrote about the need for a strong leading figure to lead the masses against social ills. He believed that people were fundamentally irrational, and should embrace their irrationality. This was taken up by fascist ideologues who thought that their members’ irrationality should be harnessed by the leader and directed into political action, which was mostly comprised of beating up socialists, communists and trade unionists (or Jews in the case of Nazism). Fascism was a fundamentally violent ideology which praised war and conflict. Both Hitler and Mussolini believed that war was the highest expression of human ability and society, and sincerely thought that life was a continual conflict between people for limited resources (hence the title of Hitler's autobiography, Mein Kampf). To fascists war was a good thing because it let nations or races decide who was the strongest and who deserved the planet's resources.
Fascism’s insistence on embracing irrationality is one thing that makes it hard to comprehend; although Hitler and Mussolini wrote their respective handbooks about fascist beliefs, they ultimately rejected concrete doctrines and always acted in response to current events. This is why a lot of fascist rhetoric and actions seem to be contradictionary.
The First World War gave fascism its mass base. Veterans across Europe felt alienated in civilian society after the war, which could not understand their experiences on the frontline. A lot of them wanted to return to an idealized comradeship and hierarchy of the front line, which fascist organizations like the SA and the Blackshirts offered. A lot of them didn’t actually care about the nuances of fascist ideology, they just felt like they didn’t belong in civilian society and needed order and comrades. Instead of a real enemy opposing army, fascism offered them a frontline against post-war society which was especially attractive in revisionist countries like Germany and Italy, where many wanted to destroy the existing Liberal order which they blamed for their countries’ humiliations.
Unlike socialists and communists, fascists wanted to cure modern society’s alienation through the creation of a hierarchal state made up of different social classes working together for the benefit of the nation. This is called ‘corporatism’ and is fascism’s only real contribution to economic thought. The competing segments of industrial society would be united by the leader act entirely through the state, which incidentally would preserve existing capitalist hierarchies and strengthen them. Fascists were for a sort of inverted social-democracy which would give social services to its members but not to anyone else. If you were not a member of the nation or the Volksgemeinschaft - tough luck. This is why many people participated in Fascist and Nazi organizations like the DAP or Hitler Youth; if you did not actively participate in the national or racial community, you were not a part of it and would be socially ostracized (or worse) and denied state benefits. They didn't necessarily believe in fascist ideology, and many opposed it, but the fascist state required them to participate in it.
The major difference between fascism and socialism is that the former was all about preserving hierarchy and bourgeois society, while getting rid of industrial alienation through the creation of a totalitarian society. Mussolini thought that by giving up your individuality to the totalitarian state, you could have your energies and efforts multiplied by its services. Paradoxically, by surrendering individuality, alienation would somehow disappear. In industrial societies, fascism was popular with the middle class because it offered a cultural and social revolution which would keep hierarchies and fortify them through corporatism. Unlike conservatism, fascism wanted a cultural revolution that would create a “New Fascist Man” who had no individuality separate from the state. This is why it was appealing to the middle class; it let them vent their frustrations about modern society and be little revolutionaries while simultaneously protecting their property and position in the social hierarchy.
The emphasis on maintaining private property and hierarchy was what made fascists hate socialists and communists. Fascism marketed itself as the “Third Way” between Liberalism, which was responsible for alienation and the post-war Wilsonian order, and Socialism, which threatened to take bourgeois property in an economic revolution. Conservatives and fascists usually got along because they both hated the same things, but most conservatives failed to understand the revolutionary aspect of fascism and believed they could be controlled to curtail workers’ rights and revise the Paris Treaties, which didn't really work out.
EDIT: I've got to go to class right now, and I'll try to answer all your questions ASAP!