See Documentation/ directory, for further instructions:
readme.1.compile-ROMS - Info on getting roms to compile on your machine.
readme.2.model-setup - How to configure roms for your specific simulation.
Relevant:
Documentation/ - Your next step for more info...
src/ - The latest roms code is kept here. Do not modify code here! Use Work/ directory.
Examples/ - Collection of working examples, both realistic and analytical.
Tools-Roms/ - Pre & post processing tools can be compiled here.
Work/ - Edit roms files here and compile simulations here.
Less relevant: (you're unlikely to use these)
Legacy/ - Old code no longer used in latest version of ROMS.
NHMG/ - Non-hydrostatic modules