This is a very basic question, but I'm confused on what the difference is between the DEM and SLOPE files. And what data constitutes a SLOPE file.
Each data value in the DEM file is the mean elevation of each cell. Each data value in the slope is the slope of each cell. It is generally derived from the DEM file. The units of the DEM file must be meters (generally with an NAVD88 vertical datum) and the units of the slope file must be degrees. The slope is relevant because SLAMM can calculate partial cell conversion (and sometimes hydraulic connectivity is affected by the slope as well).
See the section on Input File Requirements in the Tech Doc. Best regards!
-- Jonathan