Monism and Dualism are both philosophical beliefs of some people. Both Monism and Dualism do not believe the same thing. We can as well say Monism is the direct opposite of what Dualism stands for. To get this better, let's look at some differences between them. Monism is a type of doctrine that believes in oneness and unity of reality. Monism believes there is no significant difference between the individual self and the supreme being.
It seems the creator of the whole world and person as one. This type of belief can be likened to atheism. Dualism, on the other hand, believes that there is a big difference between self and the supreme creator, such that they think of the supreme creator as the most powerful. Monism also believes that all living beings are created with the same soul as the supreme being.
Monists believe the individual soul is as powerful as the supreme soul. However, Dualism doesn't believe in such, it believes individual souls are made less powerful compared to the supreme soul.