1. You must set something (a drive or a folder) to share on each computer
2. You must set your firewalls to allow communications with the other computer.
If your router has an IP address of 192.168.0.1 and your computers 192.168.0.2 and 192.168.0.3 you must set all the firewalls to allow communications in the range 192.168.0.1 - 192.168.0.3