Before you can subscribe to an existing library, you need to define the Local Content Library.

To create a Local Content Library, proceed as follows:

1. From the vSphere Client, access the vCenter Server and, from the menu, select Content Libraries and click on the create a new library icon with the + sign to open the create library wizard.
2. Enter a name and a description in the note field, then click Next.
3. Specify the type of content library you want to create (local or subscribed), then click Next. Select Publish externally to make the content of the library available to other vCenter Server instances. If you want the users to use a password when accessing the library, select Enable authentication and set a password. Check the Optimize for syncing over HTTP checkbox to create an optimized published library. This library is optimized to ensure lower CPU usage and faster streaming of the content over HTTP. This library is used as a central content depot for subscribed libraries:

4. Select the datastore used to store the library's content and click Next.
5. Review the settings and click Finish to create the library.