The easiest way is to set the Virtual Machine's Network Adapter to Bridged (have a look at 
Configuring the Network Connection), this way it's a direct peer on the same Subnet the other Windows 8 system is on. This is of course assuming the Host is also on the same Subnet as the other Windows 8 system you want to access from the Windows 8 VM.
Okay, that's about it from the VMware Fusion side of things and the rest is a normal Windows issue and should be addressed accordingly. If you do not know how to share and do Networking in Windows then consult the Windows Help Files or have a look at: How to Network Windows 8 | PCMag.com