Set Credentials: This is used to enter the credentials used to connect to the external data (example analysis db) from the excel sheet.
Target Application Administrators :
The list of users who have access to manage the Target Application settings. The farm administrator will have access by default.
What is meaning of target application here? Is it the secure store app or the excel app? Suppose lets assume target app is the secure store app. Then, when I add a user here, lets say this user is not a member of farm admin group. Then this user will not have access to central admin, thus no way to reach this secure store application for any management. What is purpose of this ?
The users and groups that are mapped to the credentials defined for this Target Application.
Who are the members here?