Start the ‘application’? Which application are you referring to? The OpenSprinkler firmware compiles in command line (just run the build.sh script), and runs in the background and it’s essentially a HTTP web server. By application do you mean the user interface? You can access the web server by either typing in the IP address:8080 (where 8080 is the default HTTP port of the firmware), or by using the OpenSprinkler mobile app (again, put in ip address:8080 to the app)
I have no idea what OpenSprinkler.launch is. Also, OpenSprinkler firmware does not require a GUI (no X required).