Quick PHP question, variable passing from html into php

I want to have a variable passed on from an html page, to a php form. Or, have a variable sitting in an html form (I have the html form created), and then when it is submitted, this variable gets passed to the php script as well as the form information. Also, how could i get a second variable passed from an earlier html page to the html form? (or php form)

I’ll try to describe it better:

Viewer comes to an html page. Then they wish to go see the form page. When they click to go to the form page, a variable has to be passed to the form page, I know it can be done as www.newlocation.com/?variable1=101 or something like that, now, how can I retrieve that variable so I can pass it on once the form is filled and submitted? I would really appreciate any help, I know this is probably a really dumb question, but i’ve never done it before. Thanks!!!