Synthetic cannabinoids refer to a growing number of man-made mind-altering chemicals sold as shredded plant material. These substances are supposed to provide the user with the same effects as cannabis, but they are often much stronger; the potency is difficult to measure. Typically they produce a pleasant state of relaxation and of feeling “stoned”. These NPS act like Cannabis, THC
Examples are ‘Spice’, ‘Noids’ or ‘Black Mamaba’.

Short term risks include psychosis, confusion, cognitive impairment, renal failure, hypertension and seizures.
Long term risks include an addictive potential, psychological depedencies and psychotic illnesses. Not all long term effects are currently known

Cannabinoids are commenly smoked (sprayed over a mixture of plant materials) or inhaled with a vaporiser.

For more (fairly technical) information on the different cannabinoids, you can visit this Wikipedia page. Be aware though, that this page is not scientifically checked.

Source: 1, 2, 3