The A320 should come with its own set of emulators pre-installed. There are also many community developed emulators you can download and install.
To play games, you will need to download roms and place them either on your A320's internal memory (NAND) via a PC and the supplied USB cable (the A320 will be detected like a regular flash drive) or if you need more storage space you can use a Mini SD card.
You need to pay attention to the format of the roms. Most need to be unzipped and some require conversion to a special format.
Roms should go in the 'Games' folder, you can create sub folders if you like.
Check the link in my signature for some useful information to help get you started.
