The ArcGIS Online World Geocoding Service allows you to find addresses or places in the world, geocode a table of addresses, or reverse geocode a location without the need to purchase the reference dataset for creating the locators. The service references rich and high-quality point and street address data, places, and gazetteers that cover much of the world. The World Geocoding Service is widely available—all you need to access it is an Internet connection and the proper credentials—which may make it unnecessary for you to set up the service on your own instance of ArcGIS Server. The service is intended to simplify the workflows of developers and GIS professionals.
The World Geocoding Service offers quick access for finding addresses or places interactively without requiring an ArcGIS Online for organizations subscription. The service is added to your map as a default locator and is available on the Geocoding toolbar or the Find dialog box.
For geocoding a table of addresses, rematching a geocoded feature class, and reverse geocoding a feature class, the service operates under a credit-based usage model that allows you to pay only for what you use. If you don't already have a subscription, you can purchase one or request a free trial. For more information on the credit-based usage, see service credits for geocoding.
To sign on to ArcGIS Online, click File > Sign In in ArcMap or ArcCatalog.
When running the geocoding process that requires a subscription, you will be prompted to log on to your ArcGIS Online for organizations account using the ArcGIS Online Sign In dialog box if you aren't signed on already. 
Once you sign on to ArcGIS Online, you can browse to the World Geocoding Service in the Catalog window under Ready-To-Use Services > Geocoding. You can select this service when you are prompted for a locator using the geocoding geoprocessing tools.