The Nicolaitans were a minor, short-lived heretical faction within the 1st century Christian community. Scripture mentions them only twice (Revelation 2:6, 15) and tells us nothing about their beliefs.
Their origins are unknown. There is absolutely no substance to the claim that the Nicolaitans were so called because they were 'conquerers of the people' (the meaning of 'Nicolaus'), or that their founder was Nicolaus of Antioch (Acts 6:5), or even that his name was Nicolaus at all.
Nicolaism was limited to the Turkish churches of Ephesus and Pergumum. The distance between them was considerable (~206km) and there is no mention of the heresy emerging in other local congregations (e.g. Smyrna). We can only speculate about the reasons why it failed to spread further.
What did the Nicolaitans teach? The paucity of biblical evidence makes it impossible to be sure, but their mention within the context of Balaam's error (Revelation 2:14) has led many to conclude that Nicolaism involved the indulgence of paganism and immortality.
Unlike Gnosticism (a 2nd century heresy of leater decades) there is no evidence that the Nicolaitans believed themselves to possess secret knowledge or superior wisdom. Indeed, there is no ideological or historical connection between these two groups whatsoever.