Set up an account with Enterprise Login
There are two basic types of accounts for individuals:
Free Public Acconts
The Duke campus account is allotted a fixed number of "credits" (like a debit account) per year, which are consumed during the course of the year by using certain functions and storing data ArcGIS Online.
In our academic environment, Geocoding consumes the most credits, followed by Feature Services Storage. Tile Storage, various Network Analysis tools, and the other Analysis tools can also potentially consume many credits if not used judiciously.