Managed MetaData and document Libraries

Basic question here regarding Sharepoint Online.

Could somebody direct me to the quickest way to tag documents in a library with Managed Meta Data?

Right now, i'm downloading various excel Reports from a nonsharepoint website.  When downloading, I save the file  in a location via Windows Explorer that is mapped to the Sharepoint Online Doc library.

That's easy enough to get the document into the Sharepoint Libarary but then i have to go into Sharepoint Online, go to the document library UX to set the appropriate managed metadata. 

Is this the best currently available approach or are there more efficient processes. 

I'm personally somewhat familiar with using the CSOM in powershell if there's a better option there but also looking for something to help the basic business user.