Sociology is defined as "the study of the development, structure, and functioning of human society." while psychology is defined as "the scientific study of the human mind and its functions, especially those affecting behavior in a given context."
To put it more simply, sociology is the study of human interaction. It includes how people behave, how societies and cultures develop, and how different groups of people interact. Psychology is similar, but caters more to the biological side. You'll delve into the functions of the brain and how it shapes us as a person.
There are many similarities between the two because at the end of the day, you're studying people and human interaction. One of the fundamental differences is how exactly you do so. Sociology examines the "big picture" of groups, cultures, and societies from a social standpoint, while psychology examines the brain and biological influences that can create certain behaviors that feed into the greater groups, cultures, and societies.
Essentially, they're similar in that they look at similar issues, but from different angles. There's plenty of overlap. They're both very interesting!
Here's good information and an infograph to see the differences.