How long you are working there?
If you are new and he is not sharing anything to you, intention might be for you to observe the things like working atmosphere first. Meet your colleagues at break time, discuss with them and gather the history of the company and its policies. Communication is more important for a HR position. If you could communicate properly, it will be easy to make your supervisor to share the things to you.
If you are working long time and still he is not sharing details, issue might be with him. He might be feeling unsecured. In this situation, It will be little bit difficult. But you should not loose hope. You should find an appropriate time to press him to share things to you, like when he wants to go on leave or permission. You have to ask everything and need to proceed further from there.
This situation is normal in all departments. But its a fresher or a new employee potential on how he could overcome this situation.
Wait for your time and don't loose your hope. Be positive always.
Thanks.