Meditation is a conscious effort to change how the mind works. The Pali word for meditation is 'bhavana' which means 'to make grow' or 'to develop'.
The Buddha taught many different types of meditation, each designed to overcome a particular problem or to develop a particular psychological state. But the two most common and useful types of meditation are Mindfulness of Breathing (anapana sati) and Loving Kindness Meditation (metta bhavana).
It is good to do meditation for 15 minutes every day for a week and then extend the time by 5 minutes each week until you are meditating for 45 minutes. After a few weeks of regular daily meditation you will start to notice that your concentration gets better, there are less thoughts, and you have moments of real peace and stillness.
Once you are familiar with Mindfulness of Breathing and are practicing it regularly you can start practicing Loving Kindness Meditation. It should be done two or three times each week after you have done Mindfulness of Breathing. First, you turn your attention to yourself and say to yourself words like "May I be well and happy. May I be peaceful and calm. May I be protected from dangers. May my mind be free from hatred. May my heart be filled with love. May I be well and happy." Then one by one you think of a loved person, a neutral person, that is, someone you neither like nor dislike, and finally a disliked person, wishing each of them well as you do so.
If you do Loving Kindness Meditation regularly and with the right attitude, you will find very positive changes taking place within yourself. You will find that you are able to be more accepting and forgiving towards yourself. You will find that the feelings you have towards your loved ones will increase. You will find yourself making friends with people you used to be indifferent and uncaring towards, and you will find the ill-will or resentment you have towards some people will lessen and eventually be dissolved. Sometimes if you know of someone who is sick, unhappy or encountering difficulties you can include them in your meditation and very often you will find their situation improving.
The mind, when properly developed, is a very powerful instrument. If we can learn to focus our mental energy and project it towards others, it can have an effect upon them. You may have had an experience like this. Perhaps you are in a crowded room and you get this feeling that someone is watching you. You turn around and, sure enough, someone is staring at you. What has happened is that you have picked up that other person's mental energy. Loving Kindness Meditation is like this. We project positive mental energy towards others and it gradually transforms them.
A teacher is not absolutely necessary but personal guidance from someone who is familiar with meditation is certainly helpful. Unfortunately, some monks and laymen set themselves up as meditation teachers when they simply don't know what they are doing. Try to pick a teacher who has a good reputation, a balanced personality and who adheres closely to the Buddha's teachings.
Yes, it is. Meditation is now accepted as having a highly therapeutic effect upon the mind and is used by many professional mental health workers to help induce relaxation, overcome phobias and bring about self-awareness. The Buddha's insights into the human mind are helping people as much today as they did in ancient times.