There are many forms of meditation. Meditation can occur as imagery, as prayer or as chanting. These are all valid techniques to heighten our awareness of a higher plane of existence.
Meditation quiets the mind, allowing the freedom to perceive other levels of reality.
Some types of meditation have no further purpose than this, to quiet the mind. This is very therapeutic and there are several techniques to achieve this. Other forms of meditation have further uses. Prayer is designed to achieve communion with the Divine. Visualization broadens the capabilities of the mind to achieve outward manifestations of what one is visualizing.