Add in confirmation mail custom field

i created a custom field named address_piso but in the confirmation mail doesn´t appear can you tell me the php code i have to use to include it?

You need to edit the files address_template via the menu Display->Views and make sure that the have the tag corresponding to your custom field.

i have it in the template but it doesnt appear in the mails

Make sure that you do it in all the address_template files (there are several of them).