Psychology is, at its most basic, the study of why people do what they do. From belief to decision making to work performance to motivation, psychology covers all aspects of why people act in the way they act.
It's important because everything we do is influenced by our minds, and so studying how the mind works and how we use it is critical to understanding who and what we are. And think about the areas that psychology has effected us, for good or ill:
* The design of every object you use is based on how some person thinks you want it to look and perform.
* The analysis of intelligence tests lead many to conclude that some races were smarted than others.
* Abraham Maslow's hierarchy of needs has had a huge impact on how business management does it's job.
* In order to understand the concentration camp guards after WWII, Stanley Milgram ran an experiment that prompted students to administer electric shock to peers, under the simple urging of the administrator. (No one was really injured.)
* Psychologists are called in by attorneys, not just to determine the capability of a defendant, but before the trial to help predict how a jury will respond to testimony.
* Time and motion studies: that was a psychologist.
* Interpersonal relationships is certainly all about psychology
It's easy to see that every aspect of our lives, every move we make, every item we purchase, every person we smile or frown at, starts from a thought. And psychology tries to figure out why.