I need to pass a parameter from Google Adwords to my website, then if
the user performs the desired action, pass it to a 3rd site (not
mine), which will grab it and store it for me to look at later. So
here's what arrives at my site:
http://www.mysite.com?TR=brackets_word_clicked_upon (this is the
search term the user to find my Adwords ad)

The user has the option to choose several options when they arrive, or
they could wander off to another part of the website altogether (or
leave). But if they do take action before leaving the site, the search
term needs to be available to be passed to the 3rd site. It's possible
for someone to arrive at my site without having come through Adwords,
and the link to the action page needs to work regardless of how the
visitor found the site. So the existence of the variable needs to be
checked and passed along if it exists as TR=brackets_word_clicked_upon

I've found various posts talking about using Javascript to parse the
URL and somehow passing the results along, but nothing that tells me
the exact syntax for doing this. I've also seen some suggestions for
setting a cookie, but again, nothing that tells me exactly what to do
every step of the way. I have done a little programming so I do
(somewhat) understand the concept of passing parameters, but what I
really need are step by step instructions on what code to place where,
and then what, etc. Thanks!

Sharon