Hello,
Please check the below KB which will help you in limiting the access to your SRX 210's web interface.
http://kb.juniper.net/InfoCenter/index?page=content&id=KB24227&smlogin=true&actp=search
You can create the security policies as suggested in the above KB article in the same way as you configure security policies using GUI. To know more on configuring security policies using GUI please refer the below KB article:-
http://kb.juniper.net/InfoCenter/index?page=content&id=kb10140&actp=search
Thanks,
Pulkit Bhandari
Please mark my response as Solution Accepted if it Helps, Kudos are Appreciated too.