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

One hint about HTML property placeholder and the tag textarea, please make sure there is no any space between </code> and <code>, otherwise the placeholder doesn't work, for example:

This won't work, because there is a space between...