Microsoft CRM 365 upload files to Opportunity

Question

Using Microsoft.Xrm SDK I have a requirement to upload documents to Files section of Opportunity in Microsoft CRM 365:

I understand that Files refer to entity SharepointDocumentLocation and I can read/create records in this entity but I am unable to figrue outt how to upload actual file and then show a link to file in my application.

Could you please refer me to some documentation/code sample explaining how to upload documents to files?

Thanks in anticipation!