Complex sentence: The self-categorization theory is a set of social psychology-related assumptions about the functioning of the social self-concept, which is a concept of self based on the comparison of self to others, which is directly related to social interactions.
Split into simpler sentences: The self-categorization theory is a set of social psychology related assumptions about the functioning of the social self-concept. A self-concept is a concept of self based on the comparison of self to others, which is directly related to social interactions.