I'd suggest you get yourself familar with how to do create /read/update/delete of vertices and edges in Gremlin using python.
Once you're more confident with the language try and design your flask api around the needs of your app - e.g if you plan to have "person" vertices (for example) with an edge "knows" to other person vertices, it would make sense for your Api to have a create person api call, and a delete person, update and maybe list persons, etc. Similarly would make sense to have api calls to create/delete "knows" edges between your person vertices. In this whole design your vertex/edge ids would be the unique identifier of your objects, much like a primary key in a sql table or an object identifier in a nosql document