You have opened this file straight from the folder. Scout Buddy is not a static page — it has an API, a database and a login, so there is nothing for the browser to show until the server is running.
On Windows, double-click start-windows.cmd instead. Or, from a terminal in this folder:
npm install npm run setup npm start
Then open http://localhost:8787.
First run takes a few minutes while it installs, builds and loads the demo troop.
See START-HERE.md for the sign-in details and what to look at first.