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

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.