The word garnish has two main meanings:

1. To decorate food with small additions that make it look more appealing. A chef might garnish a soup with fresh herbs, add a lemon slice to a fish dish, or top a dessert with mint leaves. The garnish itself is whatever decorative element gets added: parsley sprigs, orange peels, a dusting of powdered sugar. While garnishes make food look prettier, many also add flavor or texture. A restaurant might garnish pasta with grated cheese or garnish a cake with fresh berries.
2. To legally take part of someone's wages to pay a debt they owe. If someone owes money and won't pay, a court might order their employer to garnish their wages, meaning the employer sends part of each paycheck directly to whoever is owed the money. It's a serious financial consequence that happens when debts go unpaid for a long time.

The food meaning is far more common in everyday conversation. When you hear someone talk about garnishing at a restaurant or in a cookbook, they're talking about making food look attractive and inviting.