Manivaasaga says that we glorify the Nameless One with a thousand names. The Nameless One has mercifully assumed thousands of names just to become accessible to all of us in this age. The name of God is known as a mantra when it is meditated upon. A mantra is a potent vibration that resonates with the universal Truth and can reveal the same to those who meditate on it constantly.
There are literally 70 million mantras. One of the simplest is Om. Another simple mantra is the two syllabled name Raa ma. There is the five syllabled mantra, Na ma si va ya, the eight syllabled Om Na mo Naa raa ya naa ya and so on.
Is it neccesary to know all the 70 million mantras? No. Just focus on the one which your Sathguru gives you. That mantra given by the Sathguru will reveal to you all the untold secrets of the universe.
It is absolutely true that anyone can can meditate and sing the name of God. But the proper procedure is to receive the mantra as a blessing from a Sathguru. Why is it important to receive the mantra from a Sathguru? Two reasons. First, the Sathguru has realized the full potency of the mantra by receiving it from his Sathguru and by meditating on it constantly over a long period of time. Only he who has realized the full potency of a mantra is qualified to pass it on to others and only then can the receiver realize the full potency that's inherent in the divine name. Second, all mantras are potent, but because we differ in our individual tendencies, the mantra which is ideal for one may not be the best choice for another. Since the Sathguru knows your spiritual background, he can pick the mantra which is best suited to your spiritual advancement.
Who is qualified to receive the divine name from a Sathguru? The virtuous soul who is engaged in good acts, thinks good thoughts, who is humble and who serves the Sathguru is qualified to receive the divine name from a Sathguru.