Nicolaitans. What can you tell about them?
Unfortunately, I can not tell you much about the Nicolaitans. Nobody can. The only times they are mentioned in the Bible are Revelation 2:6 and 2:15, and no explanation is given there. Apparently they were well known at the time in Asia Minor (now western Turkey).
Probably they were a group of followers of a man named Nicolas. Some commentators believe they are the same group as are later in the chapter referred to as followers of Balaam and a woman called Isabella (Jezebel). They are probably not the same as those "who hold the doctrine of Balaam" because they are mentioned in addition to that group.
Keeping in mind the general tone of the letters to the churches here in the Revelation, it is possible that they advocated both following the Christ and engaging in idol worship and all that involved. Thus they would be saying "Christianity is good, but I also need to make money. I can't engage in my trade without sacrificing to idols, and the celebrations are fun." Thus they tried to follow both Christ and money. Perhaps they were influenced by the gnostics who said that whatever you did in the body had nothing to do with your soul.
Whatever the teachings of the Nicolaitans, they were hated by God and the church. If nothing else, we can learn from them that God does not tolerate erroneous teachings, and praises those who fight against heresy.