Don't take it personal but you're question is very simple. You may want to read a little bit more about deploying files...
I'll give you a track:
your ACTION tag will have a value (e.g. TARGET1).
<form action="TARGET1" ...>
So, in your WEB.XML, you'll have two very important tags (it is not mandatory, but you should). First one will register your servlet, the second will map your servlet to a URL.
So, has you can see, the "MyFirstServlet" is a generic name you'll give in your web.xml (the name won't be used anywhere else). The URL could be anything you want. For example, in your web site is:
you'll have to type
to get your servlet running. So, the ACTION tag should be this link (absolute link or not, depends).
But, as I told you, there's a lot involved in this and it is very difficult to rapidly explain you all.
Hope this helps !