Twitter plug-in is abolished in SmartJobBoard ver. 4.2 and transfered to the main functionality of the software. It is not considered as plugin anymore but it is included in the software.
You can set up Google+ settings on the Google+ page of Admin Panel.
If you use version lower than 4.2 please refer to following article:
Google Social Plug-in allows users registering and signing in to a job board easily using their Google account.
To see the way this feature works for users click here.
To get to the plug-in settings go to Admin Panel > System Configuration > Plugins > GoogleSocialPlugin (edit).
On the opened page you will see the following form:
Select the User Group(s) that will be allowed to use Google login/registration. Use the "Control" key to choose two or more items.
Then press Apply or Save to save the settings.
Use "Apply" button to save the changes and stay on the current page.