Stealth
If the circumstances are appropriate, the GM may allow you to try to hide from enemies, slink past guards, or sneak up on someone. (80, 93)
The GM could ask you to make a Dexterity (Stealth) check: d20 + Dexterity ability modifier + proficiency bonus (if you are proficient in the Stealth skill) + other bonus or penalty. Go here for why you may have advantage or disadvantage on your check.
Your check total is either contested by the Wisdom (Perception) check of any active searcher or compared with the passive Wisdom (Perception) score of anyone not actively searching. The GM could also compare your score to a DC.
If your stealth is attempted during combat, then you may also have to take the Hide action. See the benefits of being unseen in combat.