Ideally systems would be set-up such that users would type fit2d and FIT2D would automatically start. However this depends on the system directories and the users ``path'' being defined appropriately.
On all ESRF computers FIT2D should be found in the /usr/local/bin directory, which is usually already in a standard ``PATH''. This is the recommended directory for external users as well, but for various reasons FIT2D may be in a different directory. Ask your local system administrator for Help if necessary.
(The recommended directory for the FIT2D executable on Windows system is not presently defined.)