This is small tools primary function is to connect to and serve files to some of the available target platforms for GameMaker Studio 2 (like the HTML5 target, for example). When you run a game on a target that requires the Micro Web Server you will get a new window opening as the game is served to the chosen device:
The Web Server will show a certain amount of debug information related to the files that have been served, and has a button to clear this at the bottom. You can not edit most of the other information here (as it is set through the Target Manager Devices settings, but you can change the Network Speed value. Setting it to anything other than the maximum value will effectively throttle the nework transfer speed and permit you to test games in a low bandwidth environment.