The active subscriptions part is important because if you do not have a subscription to a resource you add to a permission set, then you and your users will not get access. The rest of this article and all related articles will assume you have your subscriptions set up.
First off, you only need to be concerned about this function if you are either using restrictive mode or sending your users to MyAthens. If you are doing neither, then you do not need to allocate resources to permission sets.
You can select the resources here you want to allocate to permission sets and your users will see these in personalised lists of resources such as you would find in MyAthens. You can also specify your own links to include in MyAthens if you need to.
On the resource cards, the redirector icon can be selected to filter for compatible resources.
Each will add text to the search box such as:
You can filter this way or search by name, but not both at the same time.