To some extent there can be a conflict between federal law and state law. Typically to the extent that there is any conflict between federal law and state law then federal law controls. That is, however, not always the case because the federal government was intended by our founding fathers to be a government of limited authority or limited jurisdiction. As such, the federal government cannot necessarily legislate or pass laws on every topic that effects us. The state governments, however, have general authority to pass legislation. The restrictions on state legislation whether it be from a legislative body, an administrative body or from a Court, is that in general it cannot conflict with federal law.
See Brien Roche’s book Law 101 published by Sphinx Publishing for more information on this subject.