When the "Unfortunately Launcher has stopped" message appears, tap on the "Wait" or "OK" icon. Next, navigate to the home screen and tap on the icon to access all apps. If the issue persists, please reboot the phone (power it off and power it back on).
Note: if you have a third-party launcher installed (you intentionally downloaded a launcher to replace the default launcher), first clear the data and cache for these launchers. Go to Settings > Applications Manager and tap on the third-party launcher. Then tap on "Clear data" icon, and afterwards tap on the "Clear cache" icon. Allow your phone to finish this process and then reboot the phone. If that still does not work, uninstall and reinstall these launchers, or remove them completely to use the default launcher.