With the Hide action, you try to conceal yourself. To do so, you must make a Dexterity (Stealth) check while you're Heavily Obscured or behind Three-Quarters Cover or Total Cover, and you must be out of any enemy's line of sight; if you can see a creature, you can discern whether it can see you.

After your Stealth check, you have the Hidden condition, and your total is the DC for any passive or active Perception checks other creatures can use to find you.