It's used to describe the flag of a specific country, region, or organization. For example:
* La bandera de México - The flag of Mexico
* La bandera de España - The flag of Spain
* La bandera de la ONU - The flag of the United Nations
You can also use it to describe a specific flag within a larger collection, such as:
* La bandera de mi escuela - The flag of my school
It's important to note that "de" is a preposition in Spanish, so it functions as a link between "la bandera" (the flag) and the object being described.