Dharani are chants, sometimes intelligible but often unintelligible as the original Indian meanings have been lost and they are chanting phonetically, often felt to have protective, good fortune bringing or other special powers thought to derive from the power of the sound (more than the lost meaning). Mantra are similar, but typically shorter. Dharani are recited as part of standard Soto rituals, and in most other schools of Buddhism.
I do not recite many Dharani here at Treeleaf, for I tend to consider them too much "hocus pocus and abracadarba".
Read a bit more here ... by D.T. Suzuki