i think you need to write a basic form of your own and get it to post data to another page - once you can do that - all will become clear.
html can pass values to the server or another page using a form's post array - item on the form such as inputs have a name and are given a value by the user of the form. these name:value pairs are loaded into the array when form is submitted
a form with an <input name="color" value=""/> get used by a user who types in blue
once submitted the color can be extracted from the array by scripts like $myFavColor = $_POST["color"]