The following article explains how to view a Room Type and Rate Description while making a reservation.
Room Type Descriptions
In the Room Inventory Module (System Configuration > Room Inventory), you will find areas to update the Room Types and their Descriptions.
In the Rate Wizard (System Configuration > Rate Wizard) you have the option to add a description to a Rate Plan. This description will be viewable during the Reservation Process (as well as on eRes when guests book online)