Help!!! Please!!

if there is a hidden shared folder named" user_id "on the server named "server_name", I mapped to it use \\server_name\user_id$ from my computer. The $ sign indicates that is a hidden share. If there is a Myfile.html file in that folder, so I use IE to view it, I type "http://server_name/user_id/Myfile.html ", But at this time I don't need to add $ sign at the end of user_id, so why I don't need to add $ sign?

Any help is highly appreciated!