<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
Add database driver to pom.xml. This one below is for H2 database (reference).
<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
</dependency>
Enable debug logging for Hibernate in application.properties
logging.level.org.hibernate.SQL = debug
or in application.yml
logging:
  level:
    org.hibernate.SQL: debug
Add entity class to desired package under ${project.home}/src/main/java/, for example under com.example.myproject.domain (reference):
package com.example.myproject.domain;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import java.io.Serializable;
@Entity
public class City implements Serializable {
    @Id
    @GeneratedValue
    public Long id;
    @Column(nullable = false)
    public String name;
}
Add import.sql to ${project.home}/src/main/resources/. Put INSERT statements into the file. This file will be used for database schema population on each start of the app (reference):
insert into city(name) values ('Brisbane');
insert into city(name) values ('Melbourne');
Add Repository class to desired package under ${project.home}/src/main/java/, for example under com.example.myproject.service (reference):
package com.example.myproject.service;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import java.io.Serializable;
import com.example.myproject.domain.City;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.repository.Repository;
interface CityRepository extends Repository<City, Long> {
    Page<City> findAll(Pageable pageable);
    Page<City> findByName(String name);
}
Basically that's it! At this point you already can access the database using the methods of com.example.myproject.service.CityRepository.