Why do you need separate files? What problem does that solve for your system?
One way to move data from one table to another is to use Import Records--which can import a found set of records from one table into another table, either creating new records or updating existing records with a matching value.
But a more complete picture of what you are doing might suggest alternative approaches that do not require copying any data.
It seems like the simplest approach for me to use two separate files. I am not good at creating/understanding relationships. File A treats the records differently than File B. I don't know how to make one file create records where the layouts are not using the same records.
I know where you are headed with your logic and your solution would be better than mine, but my lack of skills limits me...
Yet the end result can actually be simpler than what you want to set up here and keeping the same data up to date in two different tables can be a real nightmare of it's own that is easily avoided if you can keep the same data in a single table. And it's also not clear whether you are really talking about different files or just different tables within the same file.
But I can only discuss this in general terms without a much more detailed understanding of what you want to do with this data.
I apologize, I know what I need to do, I'm just not always good at explaining.
My Runtime currently sets up groups of teams based on an already prepared list. This is typically provided on paper, then you just create a record (team) and add the individual players listed into the portals of each record. They are selected from a database. This is easy and works perfectly as it is right now.
But, there are times when, for instance, 40 individuals sign up to play in an event and the event director is in charge of setting up the teams. Those players need to be brought in from the database as individuals. The tournament director then evaluates that list of individuals and sorts them. This list is still individual records but each player now has a number next to their name that will eventually group them into a team. For instance, if basketball event, each player is assigned a team number and would be listed like this: 1A, 1B, 1C, 1 D, 1E; then 2A, 2B, 2C, 2D, 2E; etc.
Now this list needs to populate the team portals as in the manner in my second paragraph above automatically. My original plan was to print a list, then recreate the teams from the printed list. Not the best option, but I understand it. I've seen lots of your solutions and there is no doubt you'd have something better.
I've been trying to figure a way to incorporate this procedure into my main Runtime solution, but it just can't be. I need to create my list in one file, then export the records from that file, and import them into my main solution and fill the portals somehow.
Would appear to be the basic relationship. I see no need to add any additional files or tables to your solution.
You should already have a layout for teams and a layout for team members--the portal's table. You can also create a new layout also based on team members specifically for this purpose.
You could set up that team member table as a list view layout with a drop down list of teams. You can set up your team records and then switch to the Team Member layout where you can have a list of all team members and you can use a drop down list to select a team for each team member on that layout. Once you have selected a team for each team member, they'll automatically appear in the portal on the record for that team.