Mailmerge would be the obvious approach and is eminently straightforward if you provide the users with a Word envelope document attached to the Excel data. All they would have to do is open the document in Word and run the merge to the printer or to a new document.
Alternatively, you might like to consider
Envelope or label add-in for Word This includes envelope templates and provided your addresses are one to a line in the Excel worksheet, you can print one, a selection or all the envelopes from the dialog.