Macs are generally known to find each other on network quite easy and without any special setting.
However, there are differences between various OS X versions on supported protocols and even more if you are trying to connect pre-OSX Mac to OS X one, then there might even be a problem with supported network protocol or version and supported features of the protocol.
That is why it is essential to say what are the operating system versions of the Macs you are trying to connect?
And also it is important to know which sharing protocols and options are active in Settings -> Sharing (usually third row in Settings).
The fact that one Mac sees other means that physical connection is operational and working. Therefore, it is just a question on services and settings.
Some OS X versions refuse to connect unless user name and password is supplied, but usually it is sharing protocols and options that has to be set correctly in order to be recognized and connected.