A Mask is in the nature of an Intake screen. If you don't have a document or letter that you wish to complete now, but have saved a 'mask' containing a series of variables that you want to complete now but use later, drop down the list under the label 'Input Form Masks'. That way, you can pre-save the information for a new client or customer so that it will be ready in the Existing Records list when you are ready to create a document.