It's a feminine noun, so you would use it with feminine articles and adjectives. For example:
* "La oreja derecha" - The right ear
* "Una oreja grande" - A big ear
It's important to note that "la oreja" is a very common word in Spanish, and it's often used in idioms and expressions. For example:
* "No me hagas caso, es un secreto de oreja" - Don't listen to me, it's a secret (literally "an ear secret")
* "Estar con la oreja pegada a la puerta" - To be eavesdropping (literally "to have your ear glued to the door")
If you are trying to understand a sentence that includes "la oreja", it's important to consider the context and the other words around it.