look up html forms and learn basic php.
check this out:
HTML Forms and Input
If you're talking about hosting the landing page yourself and removing the need for the visitor to visit the advertiser, stop. You will need permission from the advertiser in order for this to work.
Unless of course you simply want to iframe the advertiser's LP. And even then, some LPs have frame breaker code to keep you from doing this.
If you're talking about basically laying your own page over theirs and cutting a hole for the submit button and text box to poke through... good luck.