How to use query string in URL to display content on the wordpress page

Simple, you can use $_GET method.

if(isset($_GET["origin_iata"]) && !empty($_GET["origin_iata"]) && isset($_GET["destination_iata"]) && !empty($_GET["destination_iata"]))
{
       echo "Flights from ".$_GET["origin_iata"]." to ".$_GET["destination_iata"]."...";
}