If you are thinking of taking the GED tests, be sure that you know your state's age requirements and GED requirements. Contact your state or local "Official GED Testing Center".
If you are 16 or 17 you will most likely need to be in a program through a High School or Technical College. Although not always. If you have a Community Based Organization (CBO) that offers GED prep, you may be able to study there as well. There may also be an age requirement for testing.
If you are 18.5 you will be able to attend an Adult Learning Center and begin testing after completing a GED orientation. Again, you need to check with your state requirements.
Another great resource is the American Council on Education website.