Start here:
Schedule file transfers (or synchronization) to FTP/SFTP server

WinSCP can actually generate a batch file template for you (as also mentioned in the above guide):
https://winscp.net/eng/docs/guide_automation#generating

As a newbie to WinSCP and FTP generally I am trying to work out a way to move a file from our server to an external server via FTP and to repeat this automatically every 15 minutes, using WinSCP.
I can make a WinSCp connection to the target folder but that is as far as I have got, and I know how to assign a batch file to Task Scheduler on the source server but I could do with some help on the batch file syntax, if anybody has done anything similar, has a script I can amend or knows a better way to do this?