What is the difference between Columns and Fields?
One column represents a set of values of a particular record field on the screen with a table view of all records in the storage. If you see a list of records this means all fields in this list are organized vertically as columns. If you click View record you will see one particular record and all fields of this record with names you have given for those columns on the storage settings page.
How to save a custom-defined list to the storage
Since a list cannot be saved as a record field, you need to use the Iterate next action along with the Save record action. This approach allows you to save each element in the list as a storage record.