The function of meditation practice is to heal and transform. Meditation helps us to be whole, and to look deeply into ourselves and around us in order to realize what is really there. The energy that is used in meditation is mindfulness; to look deeply is to use mindfulness to light up the recesses of our mind, or to look into the heart of things in order to see their true nature. When mindfulness is present, meditation is present. Mindfulness helps us to understand the true essence of the object of meditation (whether it is a perception, an emotion, an action, a reaction, the presence of a person or object).
It may be possible for you to meditate on your own, without a teacher or a Sangha, a community of practice. But it goes without saying that to practice with a teacher and a meditation community is more advisable and much easier. A teacher is someone who has had the experience of the practice, and has succeeded in it. A Sangha is a meditation community where everyone follows more or less the same kind of practice. Since everyone is doing the same practice, it becomes easier for you to practice too, because the group energy emitted by the Sangha is strong and very supportive. You can also learn a great deal from individual members of the Sangha. There are many things you may find difficult to do when alone, but in the presence of the Sangha you can do them easily.