A true name must be claimed by a birth parent. A claim is not difficult, they must state that they are giving you a name and then call to you with it. Many cultures have naming ceremonies which officially mark this occasion, but a ceremony is unnecessary, and in some cases, dangerous.
Many of us do not have a True Name, our souls float, unclaimed, in the ether, vulnerable to dark powers. Maybe your mother died during birth, or maybe she just despised you.
Without a true name, you are in the gravest danger. A shamans ritual can claim your soul with a name of his choosing, forever enslaving you. His death is your only release.
Your true name is imprinted on your Soul. If you die it can be used to call you back into rebirth or resurrection.
If you are reborn, the true name from your previous life is still a valid true name, but knowledge of it will most likely be lost to you. At rebirth, it is possible for you to obtain a new true name but knowing any of the true names of any previous birth is equally as dangerous.
If you are lucky enough to have a True Name, keep it secret, for if it falls into the wrong hands it can be used to destroy you as surely as if you did not have one at all.