You can set access by enabling editing (“Turn Editing On”) on the course dashboard where the resource is originally located. Clicking a plus sign icon will open a list of the available resources. Locate the activity, hit “Edit”, then “Edit Settings” to obtain access. If the resource is hidden, click on “Show” to make it visible.
Keep in mind that creating a URL for a resource will give access to anyone who gets hold of the URL. Adding the resource to a course will not reveal the original URL.
Moodle does not offer a centralized list of their public resources. A good practice is including your resource in the Moodle site Main Menu. Check your Moodle Main Menu access permission with the site administrator.
According to How To Moodle, the ability and the process to share Moodle resources is also valid for Totara LMS users. I cannot personally confirm. But if true, it is likely that it holds for versions prior to Totara 9.
Do you have resources with open access in your Moodle Main Menu? Share your Moodle with the community in the comments!