There is a brief description of how to connect to the WebPortal in the documentation: https://docs.knime.com/2018-12/aws_marketplace_server_guide/index.html#_testing_the_deployment
In short, you need to make sure that the KNIME Server instance has a public IP, and that the security group that the machine is launched in allows access on port 80, or 443.
Users then connect via the browser to the WebPortal.
If users can connect via the WebPortal, then they will also be able to connect via the KNIME Analytics Platform in order to upload new workflows.
We’re following up about your RMI question in a related thread: Waiting for executor - while i shedule workflow - workflow not executing !! perioulsy it was working