Stamina will be an essential part of the game in two ways. It will allow you to sprint and is also required for basic attacks. Managing your stamina will be crucial to winning a match.
When sprinting, your stamina will drain, and while stamina is not being used, it will slowly refill. If the stamina bar goes to zero, you will need to wait for the stamina to refill before you can use it again.
The other way stamina will be used is through basic attacking. Every time you use your sword, shield, or throw a spear, your stamina will drain. Once your stamina reaches zero, you will no longer be able to attack until you regain some.
Drafting behind another player will also produce a speed boost as well as recover stamina more quickly.