New to this, if I write G-code but don't have a machine how can I check it to see if it would go to a machine by using two computers.

You can download and install the Mach3 machine control software and run g-code on it. To install it in simulation mode, install normally, and near the end of the install, when you see a checkbox that says "install driver", UNCHECK it.
Then feel free to play around with it all you want,

www.artofcnc.ca