I have a simple Yesod web app.
I could follow the instruction in http://www.yesodweb.com/page/quickstart, and checked stack exec -- Yesod devel
is working fine
As far as I know, the executable should be in the build subdirectory of your project directory. I think it's a hidden directory (name starting with a dot) so you may need to run "ls -a" to see it.
To run - simply execute the executable :) (Append '&' to make it run in the background).
Once you have the final version you wish to go into production with, you'll probably configure the executable to start automatically when the VM boots, to detect if the executable crashed, etc.
Good luck, Michał