Under Unix you are best of doing the following, all at the Unix command prompt:
If you can do steps 3 and 4 to solve the transport model (see the tutorial section of the GAMS User's Guide for more info, you can download this from the Web if necessary), GAMS is installed correctly.
Now, to solve your model, you will need to ftp your files to the Unix machine and run GAMS in the same way. If you want to test a MIP from the model library, do
gamslib magic gams magic
As far as looking at output, etc., that depends on what system tools (editors, print queues, etc.) your have installed there. Every Unix system will have vi, but after that it is harder to say for sure.