Customers (Companies), Contacts and Addresses are maintained in the CRM (Customer Relationship Management) Module.  To access the CRM, click the fast access "CRM Button" on the left side of the main Presidio frame.  The CRM button is white with a silhouette of 2 people.  When selected, a list of your customers will appear (below).  This list can be personalized user by user (columns selected and sequence).  This list also includes built in filtering and advanced lookup options (via lookup menu).  Right-click or double-click any record to view/edit.