In html, any control which is part of the form posts a value back using the name of the element as the key. All post back mechanisms in ASP.Net use this at the core of how they work.
So for the following input:
<input type="text" name="txtTest" value="myValue" />
You can also find the value on the server side here after the post back:
Request.Form["txtTest"] == "myValue"
This is how every control uses the postback to send data from the html form to the server.
Beyond this you'll have to provide more detail in your question about what you're trying to achieve.