A Last Will and Testament allows you to control what happens to your estate (your money, property, and other assets) after your death. In a will, you can define assets, name beneficiaries, assign guardians for your minor children, and appoint an executor to carry out your wishes. If you die without a valid will, the fate of your estate is put into the hands of the probate court.
Once you make your will, you can make it legal by signing it with your witnesses. State laws vary with respect to how many witnesses are required, whether oral wills are considered valid, and other such details.