Hi, AgustinC
After you run the start.spring.io, you will get demo.zip. Exact it in your directory, so that you will have c:\users\<myname\downloads\demo
Open the project in your
IDE and you will see DemoApplication main class.
Make sure your directory is not c:\users\<myname>\downloads\demo\demo.
The reason why the main class is not found, may be because your IDE is not looking at the right path.