Sithism is a philosophy based off of the mannerisms, behaviors, and beliefs espoused by the Sith, a fictional organization in the Star Wars Universe. The Sith represent the Dark Side of the Force, revolving around the ideal of power, specifically self empowerment. In the movies, games and books, Sith are shown as beings of evil, who kill and manipulate however they please, though this is a very simplistic representation for the sake of story-telling in the actual media series. Sithism in the real world is a much more complex philosophy, and its adherents are generally less inclined to such simplistically violent behaviors.
Sithism is a rather recent phenomenon, and one that is closely tied to the rise of Jediism, or Jedi Realism, a philosophical/religious movement based on the actions and beliefs of the Jedi, another group in the Star Wars universe who are representatives of the Light Side of the Force. In many ways, the origin of real life Sithism was a kind of reactionary movement in response to Jediism, though it is nowhere near as popular or well known as its counterpart.
Sithism revolves around two central ideas, Empowerment and Individualism.
Sith seek power, whatever that may be. The Idea of Power varies from individual to individual, such as physical strength, superior intellect, the power to have others work for you behind the scenes. An important aspect of the Philosophy is to be able to exert your influence in some way. Another aspect of this is the fact that this power is for you, and you alone.
Sith seek power to better themselves, not better humanity in general. Though one may certainly use their abilities and skills to help others, the focus is purely in your benefit, those who get something out of it are side effects. One must always consider their well being, their benefit, and their own safety before all else. This power should not be abused, however. If you spurn everyone around you, eventually it will come back to get you.
It is worth noting that in the real world, Sith are just normal human beings; we do not possess superpowers as in the movies or other related media, as this is simply impossible in our world. That being said, due the physical and mental conditioning that one may seek in their Sith path, we may sometimes be more able to resist things like pain, stress, and other things due to training, though we’ll never have powers like Telekinesis, Force Lightning, or that Ilk. Also, don’t expect to see us dressed in black robes and carrying around swords, I have to stress that this is not a movie.