There are two types of official USCIS Offices:
These offices, located outside of the United States, serve American citizens and permanent residents (Green Card holders) of the U.S. in the cases when immigration-related assistance is required.
These offices, located within the United States, provide visitors with customer service and somewhat limited information, which both serve as a supplement to the services provided via the website. Field offices also handle scheduled interviews, regarding non-asym problems.
Refer to one of the following links, depending on the type of service required:
What are the advantages included in my application?