Hello, David. This is a script step which can bring up the Specify Field dialog on setup. If you don't choose a field, it acts on the ACTIVE field when the script is run.
The regular sort sets up multiple fields if desired. This is just one field, but the ability to NOT specify a field, makes it flexible to use any field.
You can choose ascending, descending (or value list). Keep in mind your active field if not based on value list, would sort oddly.