Create a Test Case in Katalium Framework
Test cases are essentially TestNG's test classes. Katalium   Framework provides an abstract class   com.katalon.kata.testng.TestTemplate with some   convenient utilities:
-      
WebDriver is initialized before each test method and can be accessed with
this.driverordriver. If the test method ends with adriver.quit()statement, a new WebDriver will be created for the next test method. -      
Page instances are also preinitialized using Selenium's
PageFactory. Refer to this article to learn more about the Page Object Model. 
Here is a very simple Selenium test (source code):
package com.katalon.kata.sample.testcase.simple;
import com.katalon.kata.sample.Constants;
import com.katalon.kata.sample.page.CuraAppoinmentPage;
import com.katalon.kata.sample.page.CuraHomePage;
import com.katalon.kata.sample.page.CuraLoginPage;
import com.katalon.kata.testng.TestTemplate;
import org.testng.Assert;
import org.testng.annotations.Test;
public class LoginTest extends TestTemplate {
  private CuraHomePage curaHomePage = new CuraHomePage(Constants.baseUrl);
  private CuraLoginPage curaLoginPage;
  private CuraAppoinmentPage curaAppoinmentPage;
  @Test
  public void shouldLogin() {
    curaHomePage.open();
    curaHomePage.makeAppointment();
    curaLoginPage.login(Constants.username, Constants.password);
    boolean exist = curaAppoinmentPage.isOnPage();
    Assert.assertTrue(exist);
    driver.quit();
  }
}