I think the end of your question is what's drawing the downvotes:
Can anyone point me to some good resources to understand the
technology behind it?
Questions on Stack Overflow are expected to be specific, clear, and have a right or wrong answer. Questions asking other people to provide you with good learning resources will almost always be closed, and likely downvoted.
It looks like the first part of your question was downvoted too:
Does the html website tell the browser what to send back after the
user clicks something or what? I've been monitoring button presses
with wireshark and the message it POST back doesn't seem to be in the
I can't read the minds of the downvoters, but I think this question was a bit unclear, and showed little effort. I'm guessing writing this question a little more clearly, with more information, might have helped. Something like:
I'm looking at the post packets in WireShark that come over after
I click a submit button in my form, but I don't understand how certain
parts are generated based on the html in my form.
Then provide a screenshot from WireShark, the specific piece of the packet your confused about, the html from your form, etc.