Sorry, this is rather vague. Do you want to upload only the new files? Or will there ever be files that you do not want to upload? How often do you want to monitor the folder? Periodically? Continuously?
These are related:
https://winscp.net/eng/docs/guide_schedule
https://winscp.net/eng/docs/task_keep_up_to_date

I am new to WinSCP, I need to monitor a Windows directory and when a file appears send it to an SFTP location. There will be three files put in that directory daily. What is the best and most straightforward way to accomplish this? Any help or advice would be greatly appreciated.