Albert,

Rather than trying to describe all the steps necessary to eventually end up with an envelope template you can use, that doesn't use text boxes (and most do), I am simply going to offer one I have created:

Commercial #10 Envelope Template without Text Boxes

This will download as an MS-Word document template (DOTX) file.  Selecting it and activating will cause a fresh copy of an envelope to open in MS-Word ready for addressing.

There are three lines of text I have as place holders for the return address:

Return Line One

Return Line Two

Return Line Three
Selecting from the R in Return, to the end of the line, then typing the Name, Street Address, and City/State/Zip for lines One, Two, and Three, respectively will get you a return address properly sized and positioned.

There are three lines of text I have as place holders for the main address that are centered horizontally and vertically on the envelope:

Main Address Line One

Main Address Line Two

Main Address Line Three

Again, selecting from Main to the end of line for and using the same items, but for the main addressee, that were identified for the return address, will get you a correctly placed address.  Make sure not to select the spaces leading up to the word Main or the position of the address will be wrong.

I cannot tell you how to print it specifically, because how you actually feed an envelope varies from printer to printer, even within a single maker's models.  Sighted assistance would be needed just so that the actual feed information can be learned as far as which side goes up or down and which direction the flap should be oriented so that you get the front of the envelope printed and with the return address at the upper left of the envelope.

I hope this helps you, and potentially others.
--

Brian - Windows 10, 64-Bit, Version 21H1, Build 19043  

Science has become just another voice in the room; it has lost its platform.  Now, you simply declare your own truth.

       ~ Dr. Paul A. Offit, in New York Times article, How Anti-Vaccine Sentiment Took Hold in the United States, September 23, 2019