When you have done the flashing of your meteobridge and initial network setup done, you can reach meteobridge for some final configuration with your browser by typing in its IP as URL. Following sections will tell you how to finalize the configuration so that your weather data gets uploaded to Weather Underground.
Your browser will show you meteobridge's web interface with 5 tabs. Please go through all these tabs and make the required settings. The page will show warnings for all still missing essentials until you have worked through all of this. It is just a few steps, which will be explained in the chapters below, page by page.
When you can reach meteobridge web interface this is a proof that your network settings are fine. The meteobridge application code that presents the web interface is not stored in the non-volatile flash memory of the meteobridge, but gets downloaded from the Internet during boot. So without having the meteobridge connected to the Internet, this will not be there. However, once you have access to the web interface you can make changes to networking to prepare the unit to be operational in another network environment which may need different settings. To get you around the bootstrap problem (how to configure networking when you need networking already configured to be able to do changes in the configuration?) there is a meteobridge simulator in the Internet, which works as described here.