How to create a help button beside a field and provide help text.

Hi Guys ,

I have a requirement where I need to provide a small help button beside a field on web UI .On pressing this button the users will be provided with the data what to enter in the field.This data must come as a pop up .The user will read the text from pop up and close.Accordingly , he will then fill the field himself.

Here the required field is a long textarea field (like the notes field in Account details page).And how to provide the help text in pop up.

One more question :Is there any other way to help user enter this text field..?The user only wants some help to fill out the fields.He will not select any value.

This is how the field will look.I want to give a help button left side of this field and then the help texts should come on click.

Awaiting response.