Psychology is the scientific study of human behaviour, experience and mental processes. It places emphasis on the individual: His behaviour, his experience, his perception, his cognition and it’s relation to his social surroundings.
On the other hand, sociology is the study of people in relation to their culture or environment. It focuses on group dynamics and societal behaviour.
Psychology and sociology can be understood as two sides of the same coin. Both aim to understand human beings better. Only their approach is different.
Psychology and sociology do meet at one point, namely in the sub field of social psychology. Social psychology studies human behaviour and cognition in the social context. It is like psychology as the emphasis is on the individual and also like sociology as it studies group phenomenon and dynamics.
It is interesting to note that Wilhelm Wundt, Father of modern psychology proposed two pillars of psychology: the experimental individual psychology and folk psychology. The first is the one which we refer and study as psychologists. The latter involves studying group dynamics and individual-group interaction, similiar to sociology.
With this I conclude that depsite the differences in both disciplines each can provide invaluable insights to the other.