Lightsabers are the weapon of a Jedi, Light, Dark, or otherwise.
How They Work
By using special crystals and a complex hilt, A beam of cutting light (much like a laser) is generated in the shape of a sword. Lightsaber blades can cut through almost anything, excluding other lightsabers, Cortosis (which shuts down a lightsaber), PhrikAlloy (which resists lightsabers), and Mandalorian Iron (which resists lightsabers).
Obtaining A Lightsaber
In the Dark Brotherhood, a member is not permitted to have a Lightsaber displayed on their Dossier until they have reached the rank of Dark Jedi Knight. Until that time they are permitted the use of Training Lightsabers, provided they meet certain criteria. These lightsabers are not as powerful as the regular ones, but are a valuable training tool.
When they are knighted, they are allowed to fabricate their lightsaber using a special, web-based tool which allows them to pick through many different hilts, colors, and blade colors.
Custom Lightsabers
At the rank of Krath Archpriest, Sith Battlemaster or Obelisk Prelate are permitted to fabricate their own lightsabers from raw parts. This is commonly called a 'Custom Lightsaber', in that they are generally very unique to the user, and hand crafted.
The Herald is the Dark Council member who is responsible for creating and uploading custom lightsaber images.
Combat
Fighting with lightsabers is a test of skill. Many millennia have passed in generation of very specialized and effective forms of Lightsaber Combat, including methods on how to fight with Dual Lightsabers and the Saber-Staff.
Even more rare than those who have the training to use two lightsabers at once, or use the double-sided lightsaber, are those few who have been awarded the Golden Lightsaber Award.