The difference between sociology and psychology, generally speaking, is the difference between the group and the individual. Sociology focuses on the ways in which groups affect people and their behavior while psychology focuses on the individual-level influences on behavior.
For example, if you wanted to explain why I have a certain set of beliefs, you could go at it a couple of different ways. A sociologist might look at what sex I am, what race, and what income level. They would try to explain my behavior based on those factors. A psychologist might look at my place in my family's birth order, my relationship with my parents, and other personal attributes like that.