Don't leave others guessing—let them know exactly your expectations.
When granting authorization, it is often a good idea to communicate exactly what you want. Giving precise instructions now may save a great deal of correcting later.
Given the particular circumstances, however, you may wish to simply outline the main responsibilities or objectives with the promise of additional information and training to come.
Either way, the ultimate letter of authorization must be very detailed and specific so that the reader knows what to do, when to do it, and what means to use, and so that all such particulars are documented in order to mitigate liability. It is important that the person understand exactly what you expect of him or her.
When writing your letter, be brief and businesslike, but specifically state the details of any agreement into which you may have entered. Do not assume anything that is not explicitly written.
Be sure to state the time frame so there will be no misunderstanding as to the scope or duration of the authorization or additional responsibilities.