I believe that paragraph describes an intermediate technique to create portal (related) records. It is not necessary, and, in my opinion, does not really belong in a paper for "novices". There are easier ways.
If the portal is not sorted, and the relationship is simple, just turn on [x] Allow creation of related records in the relationship.
If the portal is sorted, use something like his technique. Capture the ID of the parent record (say in a script Variable), go to any layout of the portal's table, create a record, set its parent ID to your variable, return to original layout, go to field of portal. The newly created record would be the 1st, as whatever field you're sorting by would either be the latest (if sorted descending by timestamp) or blank (which sorts to the top).
People & Roles are "parent" tables; Assignments is a "join" table. This little example file is a generic join example, without a sort, just simple [x] Allow creation in the relationship.
Thanks Fenton. Your sample was very helpful. I've got it working now. I guess it's just a matter of getting my head around doing all this 'programming' through a GUI. I was working from the concept of INSERT INTO.... WHERE... but that doesn't seem to be how this is structured.
I'm still only seeing numbers (primary keys) in my portal though. I'm using value lists based on other tables and have indicated that it should only show the second value but this seems only to work when accessing the DB through a browser on the intranet... not when using it directly in FMP.