You'll need a word processor for that. Windows is an operating system.
Microsoft makes a word processor called Word. I know ... what an original name. It used to be possible to purchase Word separately but that doesn't make financial sense anymore. Now it's cheaper to get it as part of the entire Microsoft Office program, which
you can get on subscription for just 7 bucks a month.
There are lots of other really good word processors, and they all do envelopes.