IOA and OEA are clearly explained in FX2LP TRM.
This information is present in the TRM in page173:
The EZ-USB has up to five 8 bit wide, bidirectional I/O ports.
Each port is associated with a pair of registers.
■ An ‘OEx’ register. It sets the input/output direction of
each of the 8 port pins (0 = input, 1 = output).
■ An ‘IOx’ register. Values written to IOx appear on the
pins configured as outputs; values read from IOx indicate
the states of the 8 pins, regardless of input/output
In your case:
By default all port pins are in input state, so to chnage PA.0 to output, use
The value you write to IOA will appear on output pin, for example to output 1 on PA.0, use