I've just completed updating our pdf manual for HEC-RAS 6.0. The manual includes step-by-step instructions for building, running, and troubleshooting models, with screen shots and links to free video tutorials. As a bonus, the new manual also includes a walk-through for using the new (and free!) HEC-HMS tools to delineate flow paths and watersheds for use as breaklines and rain-on-grid 2D Flow Areas in HEC-RAS. See the screenshot below for a preview of one of the chapters.