A Power of Attorney is also not like a bilateral agreement, it is more of a unilateral description of what authority is permitted by the principal.
Powers of Attorney in the United States are subject to the laws of individual states, so the document changes to conform to your particular state s laws. There is no overall federal law concerning Powers of Attorney, but there is a model Uniform Power of Attorney Act which many states have adopted, fully or partially.
Power of attorney, also referred to as a POA, is a legal document that allows a person (principal) to choose someone else (agent or attorney-in-fact) to represent their financial, medical, tax, vehicle, parental, or any other needs selected. The document does not need an attorney to create (although it is always advised that a person seek legal counsel) and after completion, depending on the State, signatures need to be witnessed by at least two (2) people or by a notary public (preferred).
A Power of Attorney can help make your life much easier, by allowing someone you trust to take certain actions on your behalf. Without this document, you might not be able to travel out of town, make certain investments, or handle business or personal affairs.