Questions: Would you explain what law takes priority when. Sometimes I find that a state law prohibits something that the federal law doesn't. What law applies? How can I tell which one to follow? What about local regulations? 

Federal Law is the basis for our legal system. State Laws may be more restrictive than, but not less restrictive than Federal Law. For example: Federal Law prohibits any felon from possessing a firearm. Firearm includes handguns and rifles. If your state law does not prohibit felons from having a firearm then the federal law applies because it is more restrictive. The State Law applies when it is more restrictive than federal law. Justas local municipal ordinances take priority over state laws if they are more restrictive. 

In the above situation, if you lived in the City of Q you would not be allowed to own a gun because it was against the law for the City of Q. If you lived across the street in the City of J you would be allowed to own a gun if it was registered. If you lived in another state you might be allowed to own a gun without restriction because only State X has a registration law. 

Simply put no matter who writes the law, the law that is the most restrictive under any circumstances applies in every situation. 

Another good example are the regulations that apply to blood borne pathogens. Federal law requires the training and protection of all employees from exposure. This legislation was passed because not every state was willing to pay the added cost of mandating employee protection. Since federal law mandates the training program, monitoring program and vaccination program all jurisdictions must comply. They may pass more restrictive laws, for example holding records for 50 years instead of 25 but they may not enforce less restrictive laws (no program or training provided.)