I just managed to add a custom field in registration form thanks to an answer here: Adding custom field in default joomla 3.1.1 registration form and I'm able to add user information after adding the correct field in the mysql talble.
But now I would like to do more: i've a radio field type, and I would like that if user checks the right option a text field appears, or either, if the not correct one is chosen, the textbox disappear. Becouse I already have the radio and text fields.
Like: U drink beer?
yes--> if checked shows a textbox like: "Say us wich one you prefer!"
no --> No textbox appears.
Now I've the radio field and the text field, but the text field have to appear only with the "yes" option.
Joomla has been installed 1 hour ago, i added only language plugin. Nothing else has been done.
Thanks, and really sorry for my bad english.