How do I build an interactive form to display XML results

I am getting lost trying to learn everything at once. XML, c#, ASP, AJAX..

  Last time I did this FFORTRAN was popular haha.

 

I have visual studio, and expression web, and kompozer.

I can do basic html, and understand XML is an editable txt with a different extension.

 

I have a friend who has items on his website I can also look up and display on mine..

he built "an api" and sent me a "key".

 

I can build a form on an html page with radio buttons, and labels. I can set all buttons  as "not selected".  
As a person looks at the form and selects various radio buttons on my form,

I need to save the changes, so that  When a person finally hits the "SUBMIT" button at the end, I can  submit a request to my friends site.

When I send my form,  he sends back an XML file.  I need to display that -- hopefully on the same page as my radio button form.

 

Here is one such (valid) request:

Here is an example output from the API using your cust_key:
http://rvcomfort.com/rvp/dealers/roof_api.php?height=std&color=white&volt=120&ac_heat=ac&con_pump=n&power=std&btu=13,500&application=standard&cust_key=e14c522234aef9c7c848e3752518d0b1

 

 You guys probably do this a lot but it's new to me, so I can really use the help

(if I can get it for ONE item, plus my key, I can add the rest, as I'll understand how it works)  

 

Thank you for your time!

Happy Holidays!