How come I have to type the html extension when browsing my forums?

If I want to go directly to the advertising section of my site I have to type
www.bbqtalk.ca/Advertise.html

why can I not just type www.bbqtalk.ca/advertise ?

and why is the A in advertise case sensitive?

I dont see this with other websites.

TIA

File and directory names are case sensitive, especially on Unix-based servers (the majority out there).

Whoever created Advertise.html named it that.

advertise would be a different file or resource altogether, unless it was an alias for Advertise.html.

As far as not needing an extension goes, Google for "content negotiation".

While the domain is never case sensitive, the rest of the URL generally is (it might depend on the webserver, however). Some servers can find files even if there is a minor error in the URL, however (like this website - for instance this link to the html 4.0 reference guide has a typo in it and links to hml40 instead of html40, but it will be rewritten by the server.

Some servers also use content negociation and do not require extensions in the URL - the server will send the file with the most appropriate extension for the browser.

Another possibility is that those site you see where an address of the form http://somesite.com/advertise works might be because this is actually the address of a folder /advertise/ - the server then usually adds the slash to the address, and if properly configured sends you the default page for that folder. See mod_dir for how to set this up in Apache.