What it does
I'm not familiar with "Protector" as an official Magic: The Gathering keyword or ability. It's possible you're thinking of a similarly named mechanic, or a card-specific ability rather than an established keyword.
A few possibilities you might mean: Protection (a keyword that grants prevention of Damage, Enchanting/Equipping, Blocking, and Targeting—often remembered by the acronym "DEBT"—from a specified quality); Protector as a creature type or part of a card name; or a homebrew/custom term from a specific community.
If you can confirm which you mean—or share the exact card text—I can give you an accurate, Commander-focused breakdown including the common rules pitfalls and when it matters in multiplayer games. I'd rather not invent rules for a keyword that doesn't exist, since that could lead you astray during games.
Iconic cards with Protector
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