hello
I am reading head first
servlets &
JSP, I am stuck in the very basic stage of web application development

i.e. in the topic "mapping the logical name to a servlet class file"
I will summarize in short:
in HTML page we give "public URL name" of servlet in the <form method="POST" action="publicUrlName">, but browser prepends the context root on to the request & it looks like "POST/contextRoot/publicUrlName".
Here I am not understanding how browser is appending the context root, I read further lines in the book but I am not able to understand what exactly is context root? Why it is used? How browser knows what is context root that it appends in the request? I searched on internet but I didn't find simplified explanation
please help