You define the destination. This can be a field or a variable including the number of the repetition. Second option is the name of the function to call. This is either provided as text in quotes or picked from a calculation. The calculation can reference variables and fields, so you can define which function to call with e.g. reading function name from a field.
The next parameters are the actual function parameters. The first four are visible directly in the line, the other ones only if you click the gear. For each parameter you can specify a calculation to query value using fields or variables.
Technically this script step calls the exact same MBS function as before. For us the script step is just a bit of sugar for the script. The plugins can only provide a script step definition on startup and use the given options described in the plugin SDK documentation. We can’t dynamically change the options like presenting a popup menu with components and than a popup with the function in that component. Like CURL and than pick Perform.
As using the new script step breaks compatibility to older FileMaker versions, we will not use it for a few years in our examples until we no longer need to support older versions. But nice to have my plugin finally show up in script step list after 11 years of development. Please try it!