Need a custom web-page where students upload files into a teacher's Dropbox. I use Dropbox for Business and created a web-page with upload files from my web-page to my dropbox folder with API/C#/OAuth2, what about other people uploading into my folder?

Thanks for following up with the additional information. It looks like you're trying to use the API v1 /files_put endpoint. This does let you upload files into an account, so you're on the right track. It looks like you already have some code, but for reference the full documentation can be found here:

https://www.dropbox.com/developers-v1/core/docs#files_put

The destination path and parameters should be specified on the URL, and the file content should be supplied in the body. For example, if the folder is named "Everything is simple" and located in the root of your Dropbox, the path value would be: "/Everything is simple". 

Also, alternatively, Dropbox does have a feature called "file requests" that may address your need without you having to build anything custom. You can find information about it here:

https://www.dropbox.com/help/9090