The Lightsaber was the primary weapon used by the Jedi, the Sith, and other Force-sensitives. This outstanding weapon is powered by a Kyber Crystal, that in its natural state can generate and channel Light Force, emitting a blue or green light. The Kyber Crystal can also be bled by the Sith using Dark Force, and will it turn emit a crimson glow. The lightsaber consists of a plasma blade that is powered by the crystal from a metal base or handle. The handle also works as a switch that allows the user to turn the lightsaber on or off.
It is a weapon that requires a lot of training and mastery before it can be used in combats. Force-sensitives are able to immensely amplify the power of their lightsaber using the Force. The lightsaber was initially a weapon only used by the Jedi, and for a long time it was believed that only a Jedi can yield a lightsaber, but it was somehow adopted and modified with Dark Force to be used by the Sith. Many of the Sith are actually Jedi who have fallen to the Dark Side.
Lightsabers can be used for both offense and defense, but it was mainly used in defense because of what the Light Side of the Force is built on - peace and compassion. Eventually, as wars erupted, it was use in both ways. The Sith are believed to be better at using their lightsabers for offense because Dark Force is fueled by anger and negative emotions that are easier to maneuver than calmness and self-control that is represented by the Jedi Code.
A lightsaber can cut through almost anything including blast doors that are designed to hold of heavy fire power, and there are only a few ways to defend against a lightsaber attack - to use another lightsaber, or to use materials that can withstand the power of a lightsaber such as an Electrostaff, a Z6 Riot Control Baton, Mandalorian Iron, the hide of a Zillo Beast, armor made of Cortosis fibers.
There are seven lightsaber combat forms called From I through Form VII. Depending on the skill level and preference of the yielder, a lightsaber can be used with a single plasma blade or two, as seen being used by Darth Maul. Some even use multiple lightsabers in battle.