What is a will?
A will is a legal document setting out who inherits your estate, who administers it, and who cares for your children after you die. To be valid in England and Wales it must be in writing, signed by you, and witnessed by two people who do not benefit from it.
A will is the only reliable way to control what happens to your money, property and possessions after death. Without one, the intestacy rules decide for you, and they rarely reflect what most people would actually choose — unmarried partners and stepchildren inherit nothing under them.
Beyond naming beneficiaries, a will appoints executors, can appoint guardians for children under 18, and can create trusts. It should be reviewed after any material life event. In England and Wales marriage automatically revokes an existing will unless it was made in contemplation of that marriage, and divorce treats an ex-spouse as having died first.
The practical failure point is rarely the drafting. It is the original document. A photocopy is not sufficient for probate, so the executor must be able to find the signed original — which means recording where it is held, and telling someone.