Making a http request and reading json response from custom php script

I have been searching all day for how to make a http request to a certain link. The tutorial for scripting are few and not helping in this matter.

  1. I have a public service(user doesn’t need to be logged in) that I call from a mobile application with 2 params using POST.
  2. I read the params and I need to call a link that is formed using the params received.
  3. I need to read the json from the http request and read a certain value and return as a response.

Thank you