This tutorial will take you through how to search for a 3 word address within ArcGIS Online and to publish in a web application.
Prerequisite: Set up the what3words ArcGIS Locator within ArcGIS Online and add as a Utility Service
Adding the what3words Locator to ArcGIS Online
Drag and drop a CSV file of 3 word address onto a map
Adding the what3words Locator to ArcMap, ArcCatalog, ArcToolbox etc