Vcc is positive of power supply in and Gnd is the negative.
Looks like "record in" will be REC and GND.
No idea what the rest does.
Did they provide any data sheet?
If not and the above info is not enough, you may have to Google or Youtube for anything else.
If using AA batteries, I'd tend to use at least 3 in series to give 4.5v nominal.
If you only use 2, the nominal voltage will be right on the lower limit of 3v for the device to work and as the battery voltage drops, operation will suffer.
Edit....just checked Youtube and there are at least 8 or 10 videos there that should help.
Did a Youtube search for "ISD1820 Voice Recording"