Finding an Element by ID Selenium Java TestNG

I'm using Selenium and TestNG for the first time and I've been trying to search an element by its ID but I keep getting an "Cannot instantiate class" error. This is my code:

import org.testng.annotations.*;
import org.openqa.selenium.*;
import org.openqa.selenium.firefox.*;

public class NewTesting {

    WebDriver driver = new FirefoxDriver();

    @BeforeTest
    public void setUp() {
        driver.get("http://book.theautomatedtester.co.uk/chapter1");
    }

    @AfterTest
    public void tearDown() {
        driver.quit();
    }

    @Test
    public void testExample() {
        WebElement element = driver.findElement(By.id("verifybutton"));
    }

}

Maybe I missed installing something? I installed the TestNG plug-in for eclipse and added the WebDriver JAR files, do I need to do more? I tried following multiple tutorials but I keep getting errors, I hope someone can help. Thanks in advance!