In third person limited, the narration uses he/she/they but stays anchored to one character's perspective at a time — the reader knows only what that character perceives, thinks, and feels. It combines the intimacy of first person with the flexibility of third, which is why it's the default for most contemporary fiction.
The discipline is consistency: once you're in a character's head for a scene, you can't report what another character is secretly thinking without breaking the POV (a 'head hop'). Switching viewpoint characters between chapters or scene breaks is fine; switching mid-scene usually isn't.
'Mara watched him pour the wine. He looked calm — but she had no way to know his hand was shaking under the table.' Staying outside the other character's mind keeps the POV limited.
See also: Character voice exercises