Create a Spring Boot project

Use Spring Initializr to config and create a “Web project”.
Choose Project Management Tools, Language, Spring Boot version (DO NOT choose SNAPSHOT), and fill in Project Metadata (Group/Artifact, Name, Description, Package name, Packaging and Java version).
Click ADD DEPENDENCIES and choose the dependencies you need.

Below is an example of mine.
Click GENERATE, it will download a ZIP file of a web application with the configuration you choose.
Unzip the file and open the folder in your IDE. Here I use IntelliJ IDEA.

Modify the code in src/main/java/YourGroupName/YourProjectName

DemoProject.java

package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class DemoApplication {
    public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
    }
    @GetMapping("/hello")
    public String hello(@RequestParam(value = "name", defaultValue = "World") String name) {
      return String.format("Hello %s!", name);
    }
}

The @RestController annotation tells Spring that this code describes an endpoint that should be made available over the web. The @GetMapping(“/hello”) tells Spring to use our hello() method to answer requests that get sent to the http://localhost:8080/hello address. Finally, the @RequestParam is telling Spring to expect a name value in the request, but if it’s not there, it will use the word "World" by default.

Run the project
Open the browser, and enter http://localhost:8080/hello, you should see Hello World now.

If you add ?name=YourName to the end of the URL, you will see Hello World being replaced by Hello YourName on the page now.