Hi Laura,

JanusGraph support for loading data does not go further than the Traversal API (used in https://tinkerpop.apache.org/docs/current/reference/#addvertex-step ) and the JanusGraphManagement API (used in https://docs.janusgraph.org/basics/schema/ ).

A better resource than the reference docs to get you started is:
http://www.kelvinlawrence.net/book/PracticalGremlin.html

The bulk loading tips will be useful for graphs with millions of vertices and edges.

Best wishes,     Marc