Just enable the module like you normally would, though keep in mind that it depends on the Entity Reference module.
Once enabled, you'll notice that a new field called Editors (field_editors) has been created on the Article content type. You should see it under the Authoring information group. With that field you can reference user entities that should have access to a given node.
Keep in mind that the users you reference should not already have permission to edit all Article nodes. Otherwise this is kind of pointless.