Endurance points (EP) are your character's ability to perform physically exhausting tasks, such as walking, running, punching, kicking, engaging in combat, crafting, and checking how much coin is in your purse. Having high endurance is vital when locked in combat. If you're too weary to attack, you leave yourself open to be swiftly and brutally thrashed by whatever it is you're fighting. As with HP and SP, your max EP rises as you advance in player levels and guild levels. There are also some bloodjewels that will raise your max EP or even help you regenerate EP faster than you would normally.
For a tradesman, running out of endurance results in the task becoming much more difficult. You will not be able to craft while your endurance is below 1.
There are numerous combat styles and crafting styles that require varying levels of endurance to be able to properly execute while fighting and crafting. While each one offers a different and unique benefit, they are all much more exhausting to manage, and require time and practice to better yourself in each one.
You can check your current HP, SP, and EP by typing hp in game.