www.wysiwygwebbuilder.com

Could you tell me a tutorial on how external clients can send me files

Att.,

Fausto Vidal

There is no tutorial but if you already have a form you can include a upload object for them to send you files or they could just simply send them to you via email.

Or else maybe this will be helpful?
https://wysiwygwebbuilder.com/fileuploader.html