How to build a continuous FTP monitor and transfer

I was looking at the sample code from this doc: https://winscp.net/eng/docs/faq_script_modified_files

...but as I'm not familiar with powershell, I'm not clear how to make this for FTP transfers. It doesn't seem to define any FTP parameters at all.

Those are just code snippets.
You need to merge those into some of the transfer examples.
I assume you want download:
https://winscp.net/eng/docs/library_session_getfiles#powershell

Though it seems to me that you actually look for:
https://winscp.net/eng/docs/library_example_keep_local_directory_up_to_date