Scripted web pages are written by programmers. Accept only the work of experienced professionals, practiced in this work, and up to date with the latest security threats. DON'T ATTEMPT THIS if you are not in that category.
It pains me to say this, because it used to be a great way to get used to this sort of thing. Not any more. Web scripts are a key target for hackers, and if an amateur does it, it is only a matter of time till their site is defaced, or database stolen, or web site secretly hosting seriously illegal stuff, or worse.