In theory, meditation is quite simple. Meditation consists of choosing a point of attention and concentrating on it to "clear your mind". Emptying your brain of all extraneous thoughts is almost impossible. But it is possible to train yourself to follow your train of thought.
English speakers compare our brain to a little monkey that leaps from thought to thought like a vine to a vine. Indeed, if we observe our train of thought, we quickly notice that our attention span is short, and that we jump from idea to idea very quickly.
There are several types of meditation, some of which involve concentrating on a word called a "mantra", while others focus on a physical sensation, for example. Some require you to open your eyes and look at something, like the flame of a candle, for example.
Whatever the different types of practice, the aim is always to tame the famous 'monkey mind'.