A Will is a document which allows you to direct the distribution of your assets and personal belongings upon your death. You may choose the person who will be the personal representative (aka executor) of your estate. If you have minor children, you may also designate who will be the guardian of your children. The directives in your will only apply to assets titled solely in your name at the time of your death. Your Will does not direct the distribution of assets that have a named payable-on-death beneficiary or assets that are owned jointly.
Wills are not used to avoid probate.
A Revocable/Living Trust takes effect when you sign it and is used for avoiding probate when your assets are transferred to your trust. Since the trust is revocable, you retain control over your assets. Like a Will, you can direct the distribution of your assets upon your death in your trust and name a successor trustee to manage the trust assets.