Examples might include:
See Athletics & Acrobatics for comparison.
The Dexterity Modifier is added to attack and damage roles for finesse or ranged weapons.
The DM determines when you can hide.
PC rolls a Stealth check, contested by an active perception check by a creature looking. See Example under Passive Checks.
Creatures can passively detect you if their passive perception remains high enough.
PCs can be given away by a variety of factors, such as being too noisy.
In combat creatures are alert to signs of danger, so hiding is nearly impossible. This is generally at the DMs discretion, but can become over powered with lenient rulings. See Example.
Hidden creatures gain Advantage on attack rolls.
In a combat situation within a cluttered storeroom, with many places to hide. One character might use their Help action to distract a singular monster, or a couple of nearby monsters, in order that their Rogue might have a better change of hiding behind one of the many boxes. Because there are multiple options, and another player has helped, the rogue might no longer be rolling a Stealth Check with disadvantage (as they might normally, because everyone can see them) and successfully hide, this is also a case of an Advantage (from the Help action) cancelling out the Disadvantage of being in full view of a room of monsters.