Despite being Moriquendi (those Elves who had not seen the light of the Two Trees), they were guided by Círdan, Melian, and Elwë, and thus achieved great wisdom in their time. They spoke Sindarin, which later replaced the Noldorin Quenya as the primary language of Beleriand, and they also invented the Cirth.
The Sindar did not play an active role in the opposition against Morgoth during the Wars of Beleriand; but by the last age of the Years of the Trees, the evil that dwelt east of the Blue Mountains began to trouble the hearts of the Sindar, so that they began to consider the need for weapons and armour. They began to trade with the Dwarves of Nogrod and Belegrost, from whom they also learned smithcraft. Once armed, they drove invading wolves and Orcs from their land and had peace once more.
After the destruction of Beleriand at the end of the First Age, many of the Sindar Elves went over Sea. Those who remained in Middle-earth dwelt in Lindon or Elven-realms such as the Woodland Realm. They were happy in Middle-earth, but after a love of the Sea was aroused in them, they were no longer content.