What Is Psychology 
 
 Any knowledge discipline is hard to define. Firstly, because it evolves continuously. Secondly, because the range of phenomena it studies cannot be captured by any one definition. This is even more true of psychology. Long time back, students like yourself were told that the term psychology is derived from two Greek words psyche meaning soul and logos meaning science or study of a subject. Thus, psychology was a study of the soul or mind. But since then it has moved away considerably from this focus and established itself as a scientific discipline which deals with processes underlying human experience and behaviour. 
The range of phenomena it studies, some of which we mentioned above, are spread over several levels, viz. individual, dyadic (two person) group, and organisational. They also have biological as well as social bases. Naturally, therefore, the methods required to study them also vary greatly depending on the phenomenon one wants to study. A discipline is defined both in terms of what it studies and how it studies. In fact, more in terms of how or method/s it uses.
 Keeping this in view, psychology is defined formally as a science which studies mental processes, experiences and behaviour in different contexts. In doing so, it uses methods of biological and social sciences to obtain data systematically. It makes sense of these data so that they can be organised as knowledge. Let us try to understand the three terms used in the definition, namely, mental processes, experience, and behaviour. 
When we say experiences are internal to the experiencing person, we refer to states of consciousness or awareness or mental processes. We use our mental processes when we think or try to solve a problem, to know or remember something. One level at which these mental processes are reflected is the brain activity. As we think or solve a mathematical problem, our brain activities can be observed using different techniques of brain imaging. 
However, we cannot say that brain activities and mental processes are the same, although they are interdependent. Mental activities and neural activities are mutually overlapping processes but, they are not identical. Unlike the brain, the mind does not have a physical structure or has a location. Mind emerges and evolves as our interactions and experiences in this world get dynamically organised in the form of a system which is responsible for the occurrence of various mental processes. Brain activities provide important clues to how our mind functions. But the consciousness of our own experiences and mental processes are much more than the neural or brain activities.
 Even when we are asleep some mental activities go on. We dream, and receive some information such as a knock on the door while we are asleep. Some psychologists have shown that we also learn and remember in our sleep. Mental processes, such as remembering, learning, knowing, perceiving, feeling are of interest to psychologists. They study these processes trying to understand how the mind works and to help us improve the uses and applications of these mental capacities. 
Psychologists also study experiences of people. Experiences are subjective in nature. We cannot directly observe or know someone else’s experience. Only the experiencing person can be aware or be conscious of her or his experiences. Thus, experiences are embedded in our awareness or consciousness. Psychologists have focused on experiences of pain being undergone by terminally ill patients or of psychological pain felt in bereavement, besides experiences which lead to positive feelings, such as in romantic encounters. 
There are some esoteric experiences also which attract attention of psychologists, such as when a Yogi meditates to enter a different level of consciousness and creates a new kind of experience or when a drug addict takes a particular kind of drug to get a high, even though such drugs are extremely harmful. Experiences are influenced by internal and the external conditions of the experiencer. If you are travelling in a crowded bus during a hot summer day, you may not experience the usual discomfort if you are going for a picnic with some close friends. Thus, the nature of experience can only be understood by analysing a complex set of internal and external conditions. 
Behaviours are responses or reactions we make or activities we engage in. When something is hurled at you, your eyes blink in a simple reflex action.
 You are taking an examination and can feel your heart pounding. You decide to go for a particular movie with a friend. Behaviours may be simple or complex, short or enduring. Some behaviours are overt. They can be outwardly seen or sensed by an observer. Some are internal or covert. When you are in a difficult situation while playing a game of chess you almost feel your hand muscles twitching, trying to experiment with a move. All behaviours, covert or overt, are associated with or triggered by some stimulus in the environment or changes that happen internally. You may see a tiger and run or think that there is a tiger and decide to flee. Some psychologists study behaviour as an association between stimulus (S) and response (R). Both stimulus and response can be internal or external.

Source Introduction To Psychology 
http://play.google.com/store/apps/details?id=com.elytelabs.introductiontopsychology