If we examine our life we will discover that most of our time and energy is devoted to mundane activities, such as seeking material and emotional security, enjoying sensory pleasures, or establishing a good reputation. Although these things can make us happy for a short time, they are not able to provide the deep lasting contentment that we long for.
Sooner or later our happiness turns into dissatisfaction, and we find ourselves engaged in the pursuit of more worldly pleasures. Directly or indirectly, worldly pleasures cause us mental and physical suffering by stimulating attachment, jealousy, and frustration. Moreover, seeking to fulfill our own desires often bring us into conflict with others.
If true fulfillment can't be found in worldly pleasures, then where can it be found? Happiness is a state of mind, therefore the real source of happiness lies in the mind, not in external circumstances.
If our mind is pure and peaceful we'll be happy, regardless of our external conditions, but if it is impure and disturbed, we will never find happiness, no matter how much we try to change our external conditions.
The purpose of meditation is to cultivate those states of mind that are conducive to peace and well-being, and to eradicate those that aren't. Only human beings can do this. Animals can enjoy food and sex, find homes, hoard wealth, subdue their enemies, and protect their family; but they cannot completely eliminate suffering and attain lasting happiness.
It is a great shame if we were to use our precious human life only to achieve results that even animals can achieve. If we wish to avoid such a wasted life and fulfill the real purpose of being born human we must devote ourselves to the practice of meditation.
"Wisdom springs from meditation; without meditation wisdom wanes. Having known these two paths of progress and decline, let a man so conduct himself that his wisdom may increase.~ Dhammapada 282"
As the overall purpose of meditation is to understand and transform one's own mind, and the human mind is a very complex thing, the Buddhist tradition offers many different types of technique to work with it. This touches on the beauty of there being many ways within Buddhism, each responding to different needs.
There are techniques with objectives developing very specific qualities of mind such as the reduction of lust, the development of loving kindness and compassion, developing enthusiasm for spiritual practice and such.
However, in the quest for the ultimate aim of Buddhist practice – Enlightenment, all the techniques are directed into 2 main practices; the Meditative Practices of Concentration and Insight
Concentration Practices are those that work with one's conditioned habits of feeling, emotion, thought, perception and consciousness, gradually eliminating the unwanted and painful areas of oneself and bringing an experience of peace, calm and stability.
These sometimes involve specific reflections, contemplations, visualisations, concentration on an object etc. The main point is to learn how to keep the mind where one wants it to be - in a place which brings much benefit to oneself and others.
Insight Practices are those that use the peaceful stability of Concentration as a basis for developing deep insight into the true nature of reality. Meditation, correctly developed, will then uproot the defilements and unskillful qualities in our mind, one by one, progressively purifying our minds.
Eventually, the last obstacle, delusion is eradicated and the mind attains to Enlightenment. However, please bear in mind that this does not happen overnight as one might need to go through many many lifetimes to finally attain Enlightenment !