GiD can be used without any password, but then is limited to allow small models and until 10.000 nodes
To avoid this limitation is necessary to provide some kind of password, there are this options
Local: attached to a local computer
Portable USB: attached to a memory stick, can be used in the machine where it is plugged
Floating: for local network, installing passerverd with a counted number of floating passwords
Named user: doing login in our webpage from an arbitrary computer