There are two ways of moving or transferring documents/files into a folder:
Click on the document (hold down on a touch device) then drag and drop it into the new folder.
From the Context menu on the right hand side (3 dots) select "Move to Folder".
Note: To quickly find a document from the list, type in the name of the document/file in the Search box. From there you can use the context menu to send it to the folder of choice.