WinSCP is a brilliant, light application for Windows machines to move files to endpoints. In this case, it allows you to use SCP and SFTP on Windows to get files to the likes of Dropbox, Box, BackblazeB2 etc. with the help of Couchdrop.
First download WinSCP here
Additionally, if you need to create a private/public key combination download PuTTyGen here
1. Using PuTTyGen create a new RSA key (without a passphrase - otherwise it will be counter productive and you will need to enter in a password each time you go to use the service). See here on how to create a RSA key with PuTTyGen
2. Save the private key somewhere secure where WinSCP can also locate the file
3. Copy the public key string that was generated into https://my.couchdrop.io/manage/users (see below)