If you want to work with packages which are not in present in Maven, you can add additional repositories in a Notebook. Please follow the below steps to work with external ones such as Graphframes, Neo4J, Cassandra in Spark:
Let's say you want to download Neo4j connector to work with Spark.
1. In Notebook, go to Interpreters and click on the gear icon (top right).
2. Click on +, you will see the below screen. Enter all details including ID, URL and Snapshot(true). Also enter Username and password if you want to connect to a private repository.
3. After you add the repository, just go to the dependency section in interpreter settings and add the required package as below.
If a package is successfully downloaded, you will see a green dot next to the interpreter name.
You can add as many repositories as you need and download connectors to work with Spark.