Mapping Remote Network Drive Using IP Address, Port, and Drive Letter

Looking for a way to access my own files from anywhere am trying to map a network drive to a remote server. The server is not on the same network as the computer I am trying to map the drive on. I have the external IP address, the port number, and the drive letter on the server. I have entered http://external IP Address:Port Number/drive letter. I get an error message stating that the drive path is incorrect. I am using the network drive mapping wizard in the Computer screen. The remote server is part of a local network with 3 other computers. The external port number is assigned using my router at the remote location. The internal port number has not been changed. The server has been assigned a static internal IP at the remote location. I need help with the proper syntax for mapping the drive to the remote server. I can't get my Windows 7 machine to connect to the server. I can remote into the server using RDP using the external IP and the port number. How do I map a drive to my remote server? Please be specific as I am not that familiar with networking. I am trying to access a database on the server for use on the remote workstation. I need to map two drives to the server to accomplish this. I have been carrying the data on a portable hard drive, but this is not a good solution as I have to update the data on the server and on the hard drive and I am afraid I am going to lose something important or over write files that I need. Thank you in advance for your help.