The Supremacy Clause provides for the Constitution and the Laws created by the United States to be the “Law of the Land”, which means that the federal government holds power over any laws created at the state level. The tenth Amendment is meant for states to create laws that are not currently reserved by the federal government.
This means that states can make their own laws that the Federal Government currently does not have the power to enforce. Whenever a state proposes a law that conflicts with a federal law, the federal government will always win. For example, if a state wanted to reintroduce slavery, the Supremacy Clause and the 13th Amendment would supersede the state’s request. A state however, can make their own traffic, and criminals law, etc.
The Federal government is responsible for making laws regarding the military, money, taxes, international relations, etc. The states are responsible for state level taxes, transportation, capital punishment, family law, etc.