The link seems to be referring to the Lightning Experience. This is not in Classic.
If you want to develop it, you can query the Document object and the Attachment object.
So you can retrieve the files and display them in a VF page.
Setup your files:
1) Create Documents putting the Account ID in the Name field so you can relate them to a specific Account.
2) Add Attachments to the same Account.
Retrieve your files:
1) You can query the Attachment object and get all attachments related to the specific record.
List<Attachment> allAttachments = [Select ID, ParentID, body, Name from Attachment Where ParentID = 'Some SF Account ID'];
Query the Document object for document with the name containing the Account ID
Here is a SOQL query of the Document object. You can use the fields you need from it.
SELECT AuthorId,Body,BodyLength,ContentType,CreatedById,CreatedDate,Description,DeveloperName,FolderId,Id,IsDeleted,IsInternalUseOnly,IsPublic,Keywords,LastModifiedById,LastModifiedDate,LastReferencedDate,LastViewedDate,Name,NamespacePrefix,SystemModstamp,Type,Url FROM Document Where Name LIKE '%Some SF Account ID%'];