The Mool Mantar can be found at the beginning of the Aad Guru Granth Sahib. The original is in Gurmukhi, a script created specifically for the purpose of conveying the message of Guru Nanak Dev ji and his succcessor Gurus to their sikhs, or pupils.
This is a transliteration of the original, produced by Dr. Kulbir Singh Thind:
The Mool Mantar has been translated by Dr. Sant Singh Khalsa as follows:
ONE UNIVERSAL CREATOR GOD.
THE NAME IS TRUTH.
CREATIVE BEING PERSONIFIED.
IMAGE OF THE UNDYING,
BY GURU’S GRACE ~
CHANT AND MEDITATE
Mool refers to “origin” or “root”. Mantars are short passages, recited many times over to reinforce belief.
As far as I understand, the mool mantar (sometimes referred to as “manglacharan”) is a reference to the spirit of mankind. (Not many others share this belief)
God has no origin, so can have no “mool”. Man has origins in the spirit of the Creator and the purpose of the mantar is to reinforce the conviction of the person who recites it, in that origin. It is to unify and remove dualistic thoughts, ie to remove any doubts of origin and ultimate destination.
Hence it is understood by me as follows:
There is only one creator.
The creator’s spirit is a reality that subsists in all creation.
That spirit is the cause of all that occurs.
One should not fear.
Once should not begrudge.
One’s spirit is an image of the Lord’s.
One’s spirit is unborn, as is the Lord’s.
One’s spirit is ever-existent as is the Lord’s.
One’s spirit attains union with that of the Lord’s by the grace of the spiritual guide within.
Reflect upon this and recite with this in mind.