Concept of culture: Human behaviour is fundamentally social. It involves relationships with other people, reactions to their behaviour, and engagement with innumerable products made available to us by our predecessors. Although many other species are also social like us, human beings are cultural as well.
In the simplest terms, culture refers to "the man-made part of the environment". It comprises diverse products of the behaviour of many people, including ourselves. These products can be material objects (e.g., tools, sculptures), ideas (e.g., family, school). We find them almost everywhere. They influence behaviour, although we may 'not always be aware of it.
Let us look at some examples. The room you might be in now is a cultural product. It is the result of someone's architectural ideas and building skills. Your room may be rectangular, but there are many places where rooms are not rectangular (e.g., those of Eskimos).
You might be sitting on a chair that some people designed and built some time ago. Since sitting in a chair requires a particular posture, this invention is shaping your behaviour. There are societies without chairs. Just try to think how people in those societies would be sitting in order to do some reading.
Much of our life as human beings involves interacting with various cultural products and behaving in accordance with them. This means that culture shapes our behavior in a significant manner.