What goes in a letter of instruction? A letter of instruction is a document that lists all relevant financial information that your family members or executor need if something happens to you.A letter of instruction is a cheat sheet for anyone involved in settling your affairs. Unlike a will, this letter has no legal authority. This document gives your Successor, Trustee. Or Executor specific and detailed instructions regarding your wishes after you die or become incapacitated. Letters of instruction have become an important component in the estate planning process. Because the law deems that animals can't provide a legal receipt or open a bank account, you can't leave money to your pets themselves. Safety and security. Please be aware that forms will be displayed in a NEW browser window.