Selenium WebDriver how to insert text into field

I'm designing tests in Selenium WebDriver Framwework and I would like to insert text into fields in login box.

Here is a website http://ift.tt/1NQfrRE After click on "Zaloguj" button in top right corner, Login box appears. I would like to insert text into E-mail inputfield.

Here is my code:

WebElement emailInput =   driver.findElement(By.xpath("//[@id=\"inputFields\"]"));
emailInput.click();
emailInput.sendKeys("grzegorzrudniak@gmail.com");

After execution I get this error: org.openqa.selenium.ElementNotVisibleException: element not visible

Can anyone help me to insert text into this field? Please take a look at second input in this box, it's called "Hasło". Xpath of this two fields is the same. Additional question is how to insert text into "Hasło" inputfield as well?