How to create a label inside an <input> element?

Question

I would like to insert a descriptive text inside an input element that disappers when the user click on it.

I know it is a very common trick, but I do not know how to do

Answer 1

When you start typing it will disappear.If empty it will appear again.

        <%= f.text_field :user_email,:value=>"",:placeholder => "Eg:abc@gmail.com"%>

Simplest way...