No. You can see newsletter-style columns in your document in Word Online, but you can’t create or resize them there.
You can add and manage columns of text in Word. If you have the Word desktop application, click the Open in Word command (or Edit Document > Edit in Word), and follow the steps in Adjust column widths on a page. When you’re done and you save the document, it’ll continue to be stored where you opened it in Word Online, and when you reopen it, you’ll see the new column widths.