You should be running DSE Graph on a DSE Search node. When you create a search index in graph - a corresponding solr core will also be created. So:
schema.propertyKey('name').Text().create()
schema.propertyKey('favorite_number').Int().create()
schema.propertyKey('favorite_words').Text().create()
schema.propertyKey('a_third_thing').Int().create()
schema.vertexLabel('person').properties('name','favorite_number','favorite_words','a_third_thing').create()
//This last line is the index creation
schema.vertexLabel('person').index('search').search().by('name').asString().by('favorite_number').by('favorite_words').asText().add()
Would create a core with fields for name, favorite_number, and favorite_words (but not a_third_thing).
https://docs.datastax.com/en/latest-dse/datastax_enterprise/graph/using/useSearchIndexes.html