A Will is a document that provides instructions to your family and the court regarding your last wishes.  It is generally known as your Last Will and Testament.

Without a Will, your family and the court will not have any instructions on what to do with your estate.  The State in which you reside will have laws in place to address how your assets will be distributed.

Guardianship is a court process that allows a qualified individual to be appointed as your guardian to manage your medical decisions and financial decisions.

Probate is a court process that allows your designated representative and the court to execute your last wishes.

It depends.  The type of assets and estate planning that you have in place will dictate whether a probate can be avoided.