Adding Headers to HttpWebRequest

Question

Hi,

I was going through with HttpWebRequest Articles and tutorials.
As I come to know that we can add headers for the request and each header type is having its own meaning..
for example:

Accept-Language:da
Accept-Language:en
Transfer:f

I am too confused to understand these values, Might be each value is having its own functionaly while making a request.

So, May anyone of you can give me a brief idea that how can I use these value and where?
What are the new and other values?
If these are user-defined, then while making a requesting for the particular URL, where user needs to define the functionality of that header type.

can contact me at : [email protected]
Thanks
awaiting for your reply.