Examples for User Entity
In the Administration domain, you can get users details in a number of ways:
Getting Users 
To get the Windchill Risk and Reliability users, use the following GET URL:
URL
GET /WindchillRiskAndReliability12.0-REST/odata/Administration/Users
Getting Specific User 
To get a specific user’s details in Windchill Risk and Reliability, use the following GET URL:
URL
GET /WindchillRiskAndReliability12.0-REST/odata/Administration/Users(<userID>)
Getting Specific User’s Group 
To get the group details for a user in Windchill Risk and Reliability, use the following GET URL:
URL
GET GET /WindchillRiskAndReliability12.0-REST/odata/Administration/Users(<userID>)/Groups