Example: The controller of a player can see that player’s hand and the face of any face-down creatures they control.

Example: The controller of another player decides which spells that player casts and what those spells target, and makes any required decisions when those spells resolve.

Example: The controller of another player decides which of that player’s creatures attack, which player or planeswalker each one attacks, what the damage assignment order of the creatures that block them is (if any of the attacking creatures are blocked by multiple creatures), and how those attacking creatures assign their combat damage.