You can use the id field of the gmail to enter your email id:
See the screenshot attached:
Here the id is mentioned as "identifierId" you can use that to find the element. Here is the code that I used to do this :
WebDriver driver = new ChromeDriver();
driver.manage().window().maximize();
driver.get("https://www.gmail.com");
WebElement id = driver.findElement(By.id("identifierId"));
id.sendKeys("youremailid");
WebElement button = driver.findElement(By.className("CwaK9"));
button.click();
Hope this helps.