Instant Web Publishing is used to access a Filemaker file using a web browser. You would not need to have a Filemaker Client (or Filemaker Go) installed on the accessing computer.
Do you want to access the file using Filemaker Go (presumably?), or do you want to access it with a web browser?
In both instances you will need to have the file launched on a host computer. You will also have to have enabled (in File -> Sharing) access by that method (IWP or FM Network) to at least one account. To start with (just to debug) you need to have both workstations on the same network. Once you establish that works you can consider access from outside your network.