I'm assuming you are asking how the Na'vi mate. The mechanics of reproduction are similar to that of humans and other Terran mammals. However, their unique physiology provides the Na'vi with a level of intimacy unknown on Earth. Cultural anthropologists believe that when an appropriate mate has been selected (which can take many years), the male and female Na'vi will connect queues in an act called Tsahaylu to create an emotional bond that lasts a lifetime. The intertwining of queues is both highly erotic and profoundly spiritual, but does not in itself lead to reproduction. Once Tsahaylu is made between the couple, the ultimate in intimacy, pleasure that is unfathomable to humans, causes the somewhat unwillful sharing of the couple's good memories, and is a sign of Eywa's acceptance. If a couple can be foreseen to not have a pleasant or happy future, Eywa has been known to reverse the feeling produced by making Tsahaylu, a sign to the couple that mating would only, in simple words, ruin their lives together, and therefore prevents the mating, because of its life-long span. After the resulting embracing and kissing, the couple is sent to sleep by Eywa, and the two dream hintings of their future together. The couple will experience the pleasure of Tsahaylu from the moment of connection, until they awaken and have completed mating, and when they disconnect and return to their clan, they are mated for life.