Government work can be performed on the federal, state, or local level. The aspects that generally differentiate the levels are scope, sovereignty, proximity, and types of jobs.
The scope of a government is how much it can legitimately do within its authority. The scope of the federal government is defined by the U.S. Constitution. Federal workers deal with problems, issues, and laws impacting the entire nation, such as national defense, border security, foreign affairs, and workplace safety.
The Tenth Amendment of the U.S. Constitution delegates powers not expressly granted to the federal government to reside with the states or citizens themselves. State workers administer programs that impact state citizens, visitors to the state, and those parties seeking to do business in the state. Local governments are created under the authority of states, and local workers perform functions pertaining only to their jurisdiction, such as county road maintenance, library services, and garbage collection.
Responses to natural or human-made disasters illustrate the scope of government. If one or two houses are on fire, the local government responds. If several hundred houses are on fire, a collection of local governments with state oversight responds. If a thousand square miles of land is on fire, the federal government will likely oversee response efforts.
The Sovereignty of Higher Levels of Government
Higher levels of government are sovereign over lower levels of government, so a state cannot enact a law contrary to federal law. Likewise, a local government cannot violate state law. Workers at lower levels of government must operate within laws of their level, as well as higher levels. Local government workers must ensure their actions comply with federal, state, and local laws, state government workers operate within federal and state laws, and federal workers perform their duties within the confines of the U.S. Constitution and federal laws.
Proximity to Citizens
Local government workers live in the communities that their work impacts. If a citizen’s garbage is not collected, the trash truck driver, solid waste supervisor, public works director, or city manager could live next door and could get an earful about it. Citizens can point to a career service manager or front-line employee to fix their problem, which isn't a luxury for state and federal governments; at times, they may be lucky to find a toll-free telephone number or email address to contact. State workers who frequently interact with the public include state police officers, social workers, and driver's license office workers. Except for going to the local post office, the ordinary citizen does not have much contact with federal employees.
Types of Jobs
Any job you can do, you can almost always find a place in government to do it, but some jobs only exist in particular levels of government. For instance, firefighters are almost always exclusive to local government. However, if you're creative and think about what attracts you to the work, you can find a fit. Continuing with the firefighter example, you may discover that what attracts you to firefighting is your desire to save lives. So, if you want to save lives, you don't necessarily have to be a firefighter. You can join a branch of the military, work for the Federal Emergency Management Agency (FEMA), or join the state police force.