What is a cocina?

Cocina has several related meanings. As a noun, la cocina means both "the kitchen" and "the cuisine". It's also the third person singular present tense of the verb to cook, so it means he cooks/she cooks/you cook.

The sentence "Ella cocina la cocina en la cocina" would mean "She cooks cuisine in the kitchen."
"Cocina" means "Kitchen"