Power supply terminals
1) The third negative is probably for use as a chassis ground (like the housing of a motor).

2) The multiple terminals are for connecting subsystems in parallel.  It's just a convenience thing.  If the output current was very high then it might be for running multiple conductors but 10 A isn't very exciting.

3) The '13' and '14' terminals are the connected to an internal relay. '13' and '14' will be shorted together when everything is OK and they will be open otherwise.  For example you could use this to run a big light to indicate that power is on or maybe enable/disable another power supply.