Do you have EarthLink set up in the native Mail app on the iPad? Or do they have their own app? If using the mail app, when viewing your email, up the top to the right is an arrow, press this and you will receive some options, one of which is To Reply, press this and a Message box will open. I hope this helps, let us know if it's from another app.
The IPad Forum is a community of members from all walks of life and from all over the world coming together to share our experiences and to help each other learn about this wonderful piece of technology the Ipad. There is a wealth of information already here in the many threads we have so doing some searches will answer most of the questions you have. If then you cannot find the answer you are seeking then by all means post your question. There are many friendly and informed members here only too willing to help you.