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 it and drop it into the new folder.
From the Context menu on the right-hand side (3 dots) select "Move to Folder".
To quickly find a document from the list, type in the name of the document or folder in the Search box. From there, you can use the context menu to move it to the folder of choice.