You don’t have to register with USCIS website to check status of your case.
If you have an application receipt number, you can check the status of your case online, by simply entering receipt number in search box.
"From USCIS: To view the status of a case, please enter the corresponding application receipt number. The 13-character application receipt number can be found on application notices you have received from the USCIS. It begins with three letters such as (EAC, WAC, LIN, or SRC)."