Slot resources are used to provide time-slots that can be booked using an appointment. They do not provide any information about appointments that are available, just the time, and optionally what the time can be used for. These are effectively spaces of free/busy time.
Slots can also be marked as busy without having appointments associated. In some situations a service may have a specific set of slots reserved for specific uses, such as "walk-ins" or a specific organization has a "standing booking" for Thursday mornings. These should be represented using the appointmentType field with a specified and agreed value.
Security Permissions or specific business rules on the system could enforce that only eligible appointments are allocated to them.
Project FHIR API
This is the location where you can find your resource using a FHIR client.
Simplifier FHIR API
The global endpoint is where users can search for all resources in Simplifier. Resources have a globally unique guid Id here.