You can lend your aid to another creature in the completion of a task. When you take the Help action, the creature you aid gains advantage on the next test it makes to perform the task you are helping with, provided that it makes the test before the start of your next turn.

To confer this benefit, the assistance you propose must actually be productive (as determined by the GM).

Helping an Attacker: To productively assist a creature with an attack, you must be adjacent to the target of that attack when you use the Help action. You feint, distract the target, or in some other way team up to make the creature's attack more effective.