Note- use \n to move the control to next line.
ex-

import java.util.concurrent.TimeUnit;

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;

public class TextBox {
    public static void main(String[] args) {
        WebDriver driver = new FirefoxDriver();
        driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
        driver.get(“http://selenium-makeiteasy.blogspot.in/2014/05/if-any-textbox-is-disabled-then-how-to.html”);
        
        WebElement textBox = driver.findElement(By.xpath(“//iframe[@id=’comment-editor’]”));
        driver.switchTo().frame(textBox);
        
        
        WebElement comment = driver.findElement(By.xpath(“//textarea[@id=’commentBodyField’]”));
        comment.sendKeys(“good \n nice”);
    }
}

 

Source: http://selenium-makeiteasy.blogspot.com