NEMO: home page introduction
You will need a Unix environment with an interactive terminal (Linux, Mac, Windows/WSL). For plotting you can optionally use X-windows, though PNG or PS files can be created for off-line viewing.
Obviously you will need an installed version of NEMO, though one of the lesson episodes (#3) will install NEMO from scratch if you have its prerequisites (a C/C++/Fortran compiler, the make tool, csh/bash, pgplot, X11). It is possible to install NEMO without a Fortran compiler, and without csh, pgplot and X11, though obviously with less functionality.
Not neccessarely prerequisites, the following Software Carpentry lessons will likely benefit you in your work with NEMO: