What is Personality?
According to the Cambridge International Dictionary of English,'your personality is the type of person you are ,which is shown by the way you behave,feel and think.Personality is also defined as the "whole nature or character of a person.
How a person behaves,feels and thinks,how he conducts himself in a given set of circumstances is largely determined by the states of his/her mind.Mere external appearance or a person's speech or mannerisms are only fringes of one's personality.
They don't reflect the real personality.Personality development in the real sense refers to deeper levels of a person.So,a study of our personality should starts from a clear grasp of the nature of our mind,and how it functions.
Necessity to know our Mind
We intend to do many things --make resolutions to cultivate good habits,to kick certain bad habits,to study with concentration, to do something with a concentrated mind.Very often our mind rebels,forcing us to beat a retreat from our efforts at implementing our resolutions. A book is open before us, and our eyes are open.But the mind has started wandering,thinking about some past events or some future plans. The same thing happens when we sit for a few minutes trying to pray or think of a divine name or form. Says Swami Vivekananda:' Free! We who can't for a moment govern our own minds,nay,con't hold our minds on a subject,focus it on a point to the exclusion of everything else for a moment! Yet we call ourselves free.Think of it.
According to Bhagavad Gita, the undisciplined mind acts as our enemy,whereas a trained mind acts as our friend.So,we need to have a clear idea of the mechanism of our mind.Can we train it to contribute to the development of our personality?
The fourfold functions of the mind
The human mind has four basic functions. This can be illustrated by an example:suppose I met a person whom I had met somewhere,say, about ten years before.I try to recollect when and where I met him and who is he. From the inner recesses of my mind there begins a process of scanning, as it were, to check if there are any events stored there connected with the person. Suddenly I am able to recognize the person as so and so and finally say' he is the same person I met in such a place, et. I now have a firm knowledge about the person.

Let's Analyse the simple event.

Memory:-The storehouse of memory and impressions of our past experiences presents various possibilities before the mind. This storehouse is called 'Chitta'.It is in this storehouse that the impressions of our thoughts and actions--good and bad--are stored.The sum total of these impressions determine our character.This 'Chitta' ,again,is what is known as our subconscious mind.
Deliberation and Conceptualization:-Not yet sure,the mind examines the many options presented before it. it deliberates on several things. This faculty of the mind is called 'Manas' Imagination and formation of concepts are also functions of the 'Manas'.
Determination and Decision-making:-'Buddhi' is the faculty responsible for decision-making.It has the capacity to judge the pros and cons of things and find what is more desirable. It is also the discriminative faculty in a person,which enables him to discriminate between the real and the unreal, between what is to be done and what is to be avoided, what is morally right and what is wrong. It is also the seat of will-power so essential for personality development and hence this aspects of mind concerns us the most.
'I' Consciousness:-Appropriating to oneself all physical and mental activities ag, I eat,I see,I hear,I think,I am confused , etc., is called 'Ahamkara' or 'I' consciousness . As long as the 'I' identifies itself with the undisciplined body-mind complex ,human life is dictated by events and circumstances of the world; we become happy with pleasurable events, and miserable with adverse circumstances. More the mind gets refined and disciplined ,more does one get to know the real source of 'I' consciousness. Correspondingly ,a person becomes more balanced and equipoised in his daily life.Such a person is no longer swayed by any event or circumstances of life.
These four aspects of the mind, viz 'Manas','Buddhi', 'Chitta','Ahamkara', are not watertight compartments. It is the same mind called by different names based on its functions.
More about the Mind
The Katha Upanishad describes human personality with the help of a chariot allegory. 'Our' 'I' is represented by the master of the chariot; the body is the chariot and the 'buddhi' the charioteer. The 'manas' is represented by the reins to which are yoked the horses representing the the sense organs--ears, skin,eyes,tongue and nose--which are the five windows in a human being that give him or her the knowledge of objects in the world. The road on which the chariot travels is represented by the sense objects. The human being who identifies himself or herself with this body-mind system is said to be the enjoyer of objects or the fruits of actions.

If the horses are not broken and if the charioteer is asleep, the chariot can't reach its destination. It can even overturn and spell the death of the master. Similarly,if the sense organs are not disciplined, and if the power of discrimination lies dormant, one can't reach the goal of human life.
On the other hand, if the horses are broken and the charioteer is wide-awake , the chariot reaches its destination. Even so, if the 'buddhi' is wideawake, and if the sensory system together with the mind is disciplined and controlled , a human being can reach the goal of his life.What is that goal? We will come to it shortly. Another important activity of the mind that concerns personality development is our emotions. More the emotions are under control,healthier becomes one's personality. Emotions can be broadly classified into two types, viz attraction and repulsion. Love,administration,aspiration,sympathy,joy,veneration ,pride and the like indicate attraction. Hate,anger,fear,sorrow,jealousy,disgust,shame,etc.,are of the nature of repulsion.As long as one is entangled with the undisciplined mind,one's personality doesnot really develop.Buddhi ,the charioteer,serves as an effective instrument of self-development by controlling the emotions and raising the higher self from the hold of the lower mind.
What is Character?
Every action and thought of ours leaves an impression in our mind.These impressions determine how we behave at a given moment,how we respond to a given situation. The sum total of all our impressions is what determines our character. The past has determined the present. Even so the present--our present thoughts and actions--will shape our future. This is a key principle governing personality development.
What activities the body-mind system?
This is an important question,the answer to which will help us have better knowledge of ourselves. This question engaged the attention of ancient Indian seers and sages. They experimented with themselves--their sensory and mental apparatus --and after a disciplined quest they found out that there is a divine element in human beings, which is the Mind of the mind, Eye of the eyes, Ear of the ears and Speech of the speech. It is this divinity which constitutes the real. 'I' and the eternal element in our personality. This divinity survives physical dissolution of the body. This divinity remains latent in us as long as we identify ourselves with our body-mind and the sensory system. The goal of life,according to the scriptures and the great ones, is to manifest this hidden divinity.