Global assets are handy in cases where you want to create a single document like standard procedure, policy or process and make it visible across all of your clients.
To start go to Settings -> Asset Types, create a new Asset Type, check the Global Asset checkbox, the fields you want to display and you can then select all clients or just some to limit visibility.
Navigate to Documentation & Assets you will see the new global asset menu on the top of the Asset Types list. There you can create a new document that will visible under Tenant and client scopes.
You can also link this global document to an asset or health check
To give external users or clients access to Global Assets please follow this article and at a minimum assign View permissions for Documentation & Assets section.