CGI is not a language. CGI is a protocol for executing a script or program, and passing data to it. Any programming language which supports raw input and output streams can be a CGI.

KiXtart can be used for CGI but there are some issues which mean that it is tricky. As you are new to this, KiXtart is not a good solution for you. Search the board for previous discussions about using KiXtart as a CGI.

You also clearly do not understand the process of submitting form data. When you submit a form the target is a CGI - you need to run a task at the server to process the form data. This same process will display the thank-you page, or issue a browser redirect to a thank-you page.

The web server you are writing the pages for will already have a preferred CGI to handle forms and the like, so you should use that rather than trying to use KiXtart.

As you are at an early stage I recommend you put a bit of time into learning one of the mainstream CGIs.

If you have a choice I'd recommend PHP first as it is highly portable and very widely used. ASP is a good second choice if you don't mind limiting yourself to Microsofts IIS. PERL should be avoided. It is a great language and used quite a lot in CGI but is devilishly hard for beginners to pick up.