Each site must first be added to the account before it will be available in the study configuration.
First open the Site Manager under the Website Host menu
Second, fill in the form at the bottom of the page for each new site.
Site ID Number - This is an identifier of your choosing that might be used in the subject profile IDs (if the study is setup to use it) and the data extracts.
Site Type - Most sites in a study are "Provider" sites. Provider sites are forced by the system to follow rules of enrollment. For instance, a study must be published and live before provider sites can enroll. The other option, "Administrative" sites can be used for testing purposes, where a study in development might need to enter some test records at an Administrative or testing site. Normally, only one Administrative site is needed.
Dynamic CA's - In most cases this will be "Yes." Selecting "No" prevents all dynamic form logic from occurring for sites that have very little bandwidth. If No is selected, the study builder needs to keep this in mind when creating the study forms.
Read here on how to add sites to specific studies