You're in the right place if you want to offer metadata for searching in the portal. If you want to provide data products for the portal viewer with our spatial data infrastructure, look here.
To become a content provider for the portal you have to provide metadata for your datasets, articles or map projects. We basically support the defacto standardized OAI-PMH and the OGC CSW metadata harvesting interfaces. One of these standards should be accessible from the internet via HTTPS without authentication. If you have no catalog and standardized interfaces to your content until now, you might have a look at the GeoNetwork solution. Different metadata schemata and profiles are supported, e.g. ISO19115, but also customized ones. For special cases, also other web-resources can be harvested, but are not preferred.
Checkpoints for basic metadata
Checkpoints for extended metadata profiles
We are using an internal JSON metadata format (schema, example) for harmonized indexing and full-text search against an Elasticsearch cluster. Metadata is harvested regulary once a night from configured content providers. Metadata is annotated, e.g. with information from Gazetteers to resolve geographical locations to place names, during harvesting. So users are able to search also for places names not only for geometries.
As content provider you have to map your metadata content against the given JSON Schema. Best you are using international vocabularies for your metadata content. For example