Where and how do I 'check Drupal permissions' or 'set Drupal permissions'?
In CiviCRM , go to Administer -> Users and Permissions -> Permissions (Access Control) . Then , select Drupal Access Control . 



You will see a long list of various options, and check boxes to enable permissions for Components, Extensions, etc for various Roles.



Scroll down the list until you see the Component, Extension etc that you have installed and enabled in the list. Then, select the checkbox to add a permission to a Role. 

In the screenshot below, I've added permissions for the Administrator role for the ReportPlus extension I just added.



Save your changes, et voila! You should now see the new permissions for the Administrator role or for whichever role to which you have added new permissions.