A will is the document that tells a probate court what you wanted done with your property after you die. It names the people or organizations who inherit, appoints an executor to carry the instructions out, and — for anyone raising children — nominates the guardian who would take over their care. Without one, none of those choices are yours to make; a statutory formula decides who inherits and a judge decides who raises your children.
The practical value of a will is not that it is elaborate but that it is unambiguous. Most estates that turn into disputes do so because the document was silent on something: a jointly owned house, a promise made verbally to one child, a business with no succession plan. Writing it down converts a family argument into an administrative task.
A will only governs assets that pass through your probate estate. Anything with a named beneficiary — retirement accounts, life insurance, transfer-on-death registrations — goes to that beneficiary regardless of what your will says. Assets held in a funded trust are likewise outside its reach. This is the single most common misunderstanding in estate planning, and it is why a will is a component of a plan rather than the whole of one.
Execution formalities are set by state law and they vary: signing, witnessing, and notarization requirements are not uniform across the country. Follow the guidance for your own state rather than a general rule you read somewhere, because a will that is not executed correctly may not be honored at all.