how to invoke a servlet

I am getting a common problem of invoking a servlet. I checked many of discussions but i don't understand so please help me out.
First i tried with http:/localhost:8080 but it was not doing. So i changed port to 80
and now i wrote http://localhost/servlet/heolloworld but still not getting.
I am using pws but i stopped it initially.My tomcat version is 3.3 This is old version so is problem bcz of this?
I also used servlet mapping in web.xml file but still not getting. And i read web.xml file is in \conf but i am having that file in webapps.
so plz plz guide me

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