You set up your letterhead in FYI with information that is common to all documents (for example, for all letters). This would be anything at the top and the bottom of a letter and is used for any headers, date, addressee, address etc and also the sign-off, and sender details, and any footers.
Your letterhead is set up in FYI as Stationery. For letters these are set up as a Word document which is then brought into the FYI Stationery. This allows you to use the features of Word (such as formatting, margins, adding text and images to headers and footers with different headers/footer for the first and subsequent pages).
You may have Word documents already set up for the layouts and text and these can be used as the basis for the FYI Stationery.
Refer to Creating Stationery for Word.
Note: If you using our assisted onboarding services, the FYI Client Success team will help you to set up your practice letterhead.