To get to the Plugins page go to Admin Panel > System Configuration > Plugins page.
On the opened page you will see all plugins currently available in the system. There are 'Common Plugins' and 'Job Sourse Plugins':
Use the “Status” check box to activate / deactivate a certain plugin.
Make sure to press the “Save” button after changes in plugins status.
In the further sections of this manual you will find the description of settings you can make for all these plugins.