The full mantra honors all three aspects of Divine Mother: Hreem is everything that can be perceived by the senses, conceived in the mind (calls on Saraswati). Shreem relates to abundance (calls on Laksmi). Kleem relates to relationship (calls on Kali/Durga).
Om Hreeng Greeng Hreeng Mantra work with powerful sounds that activate wealth vibrations, universal energies, law of attraction focused specifically in money. Recite this Mantra everyday minimum 108 times and if you can repeat more Malas (1 Mala is one serie of 108 times) will be better and the results will become faster.