Email for different statuses

Hello,
We tried for some period to solve it, also reading forum, but we couldnt figure it out.

What we need is: when we change to custom made status READY customer should get email with text just for this status. Over all we need like 3 different types of emails for 3 different statuses.

How can this be achieved?

Hello,

We checked forum before we posted, and we saw that topic, but it's not clear for us. Is there any guide how to do it? We copied as it said in topic, but we don't know what to do after. Can u explain it better?

We have status READY (for example). What we should do so customer get custom email (with txt, we don't need html in it)? After we copy files suggested by nicolas where we should write text we want?