Metadata for Confluence is integrated with Comala Publishing. As a consequence, you can configure Metadata sets and fields in your draft space. When you publish content from your draft space to your target space, Metadata will also be published in the target space.
You can find further information how Comala Publishing works in their documentation.
Prerequisites for integration with Comala Publishing:
The publishing settings need to have the "Copy Properties" option enabled. This setting can be found in the "Advanced Options" section of the configuration.
The global configuration of the Comala Publishing app has to contain the prefix "com.communardo" (without quotes) in the list of property prefixes of the content properties to be copied. In current versions of the app this is configured by default.
The draft space needs to have a space homepage. This homepage is also published to the target space.