A later section of this User Manual provides a complete example of traversing this workflow, with a specific example that makes a specific choice of ARNs, decision to use specific sample software, etc.
Also this video on creating canonical experiments using the Program-it-Yourself approach (showing Portal interactions as of March 2022) may be of use. (NOTE: as of January 2023, with the Portal migrating to a new version, this video is somewhat outdated; we hope to replace it with an updated video soon, but in the meantime continue to provide it because it may still be helpful to see the overall sequence of steps - which has not changed.)