Anglers 16 years and older must have a license to fish in Maryland. Depending on what kind of fishing you intend to do, you will need licenses based on the type of water (non-tidal/freshwater, etc.) in which you intend to fish. You can get your licenses online from the Department of Natural Resources Website, or in person from a DNR service center or a sports license agent.
Check out these Frederick, MD fishing resources: