In OpenClinica, a Site is typically a location to which Subjects are assigned, although it can be a different organization to which Subjects are assigned. A Study can have more than one Site, where each Site might be in a different city or at a different institution. Event Definitions for the Study are assigned to Sites in the Study. Subjects are added to a Site and scheduled for Events at the Site. OpenClinica users are assigned permission to access information at one or more Sites, and can also be assigned to access data at the overall Study level.
Even if there is only one location for a Study when you create it, it is strongly recommended that you create a Site for it, and add Subjects to the Site rather than only add them at the Study level. By doing this, there are more options available for user permissions, and you will be able to easily add Sites in the future, should the Study expand.