Delegated powers and restrictions on states
Article I, Section 8 lists congressional powers concerning taxation, borrowing, interstate and foreign commerce, money, post offices and defence, among others. It also authorizes laws necessary and proper for carrying constitutional powers into execution. Federal functions are described through this constitutional allocation.
Section 10 restricts states in making treaties, coining money and undertaking specified military or external actions. States retain their own governments while facing limits that prevent them from acting as wholly independent countries in the fields covered.
References: [1]
Reserved powers and constitutional supremacy
The Tenth Amendment reserves to the states or the people powers neither delegated to the United States by the Constitution nor prohibited by it to the states. Both conditions matter; reservation does not mean that a state may discard every federal power.
Article VI makes the Constitution, federal laws made in pursuance of it, and treaties made under United States authority the supreme law of the land, binding state judges. That status is connected to constitutional authority, not automatically attached to every document issued by a national institution.
Institutions within a shared order
States receive equal representation in the Senate, while Article IV addresses admission of new states and recognition of public acts and judicial proceedings across state boundaries. Federalism includes both boundaries of authority and arrangements for state participation and interstate recognition.
The court systems reflect this structure: some disputes proceed in state courts and others in federal courts under their jurisdiction. These are features of the United States arrangement; adopting federalism elsewhere does not require an identical allocation of powers, finances or courts.