What does Request.Form["productcode"] do in asp.net?

Taken from the Mozilla Foundation:

HTML forms are one of the main points of interaction between a user and a website or application. They allow users to submit information to a website. Most of the time information is sent to a web server, but the web page can also intercept it for its own use.

An HTML form is made up of one or more widgets. These widgets can be text fields (single or multi-line), select boxes, buttons, checkboxes, or radio buttons. Most of the time, these widgets are attached to a label that describes their purpose.

All HTML forms start with the element of the following form:

<form action="/my-handling-form-page" method="post">

</form>

So basically when the form posts to the server, all the inputs inside the form FORMare sent to the server in a collection of key stringvalue string.

When you see Request.Form["codproducto"]you are seeing how the server is trying to read a value that was posted under the name"codproduct". For example

<form action="/my-handling-form-page" method="post">
    <input name="codproducto" type="text">
</form>