CMS Made Simple Forums

I have a form. When an user clicks on button, UDT must validates captcha and if it's right send a email. If captcha is wrong, it should be shown a message. All this must be done not sending on another page. So, I think, that it can be done calling an UDT on button click. How to make this?

If you use formbuilder and install the captcha module then you only need to check the use captcha box...