Spring Boot Java server using Maven and IntelliJ.

I have successfully set up Spring Boot server with Maven in IntelliJ, it's up and running (http://localhost:8080/actuator/health), but I need step by step help along with source code of how to fulfil the following conditions:

1. The main page should call one backend method "GetApplicationVersion";

2. The method should read the written number in the file and return it to the frontend;

3. On main page should be an string "Application version is " + received number.