In general, class conflict is something that naturally happens as long as different classes exist, because they have competing interests. According to Communist theorists like Marx and Bakunin, it is the driving force of societal change.
Marx came to this conclusion as a theory of history, based on studying the societies in Europe; he thus expected the European proletariat to overthrow Capitalism in Europe. While Europe had an Industrial Revolution and reached the Capitalist stage of history, non-European societies did not develop similarly. Still, the global economy embraced Capitalism and it has become necessary to understand it.
To actively be involved in class struggle, people need class consciousness. Class consciousness is simply recognising that society has an impactful class structure, and that the interests of different classes conflict with each other.
In the modern world, this means that the working class achieves class consciousness when they realise that their interests are opposed to the interests of the wealthy Capitalist class. This should ideally spark a revolution which destroys Capitalism and leads to Socialism, which should eventually lead to Communism.