A will is a legal document that transfers what you own to your beneficiaries upon your death. It also names an executor to carry out the terms of your will and a guardian for your minor children, if you have any.
Your signature and those of two witnesses make your will authentic. Witnesses don't have to know what the will says, but they must watch you sign it and you must watch them witness it.
A revocable living trust provides financial protection in the event you are no longer able to manage your financial affairs yourself. You can be trustee while you are healthy, but if you have a stroke or become otherwise incapacitated, your successor trustee would manage your assets in the trust.
You may recall that during the final weeks of his life, former President Richard Nixon refused "heroic measures" and received only palliative (comfort-easing) care at his home. Similarly, former First Lady Jacqueline Kennedy Onassis refused life-prolonging medical intervention before her death from non-Hodgkins lymphoma. Former President Nixon and Mrs. Onassis both retained control over their final medical care through use of a living will and a health care power of attorney.