"Clearing the Mind", is not quite correct. You cannot clear your Mind completely. The idea is to "free" your Mind of all the many thoughts you have, and leave just one. The best way is to concentrate on one object. Perhaps a little statue, or a lighted candle.It takes a little practice. But, after a while, the object "fades", and your subconscious brain "take over".
Meditation is really "deep thinking". Your conscious brain only sees and hears what you want it to see and hear. Your subconscious brain sees and hears everything; it remembers everything you touch! So it is very powerful!