Probate is the legal process whereby a will is "proved" in a court and accepted as a valid public document that is the true last will and testament of the deceased. So in other words it does the following:
Typically, probate involves paperwork and court appearances by lawyers. The lawyers and court fees are paid from estate property, which would otherwise go to the people who inherit the deceased person's property.
Probate proceedings are a matter of public record. There is no privacy when your estate goes through probate.