A13-SOM-WIFI-4GB is an expansion board for the A13-SOM-512 CPU module. It adds USB-OTG (through which the system can be powered), an RTL8188CU-based WiFi module (802.11b/g/n), 4GB NAND Flash, a connector for an A13-LCD display/touchscreen module (via 2×20-pin IDC cable), and through-hole GPIO headers with 0.1" pitch.
With this board and the items above, you can build an extremely compact Linux or Android system. See the A13-SOM-512's page for links to OS images.
Instead of connecting a mini-USB cable from this expansion board to your PC for powering the system, you might consider the 5V, 1A or 5V, 2A power supplies that have a USB connection, so you can instead run a mini-USB cable from this expansion board to either of those wall-mount supplies.
The name of this board can be misleading. It is not a System-on-Module; it is an add-on for a System-on-Module. This board does not have a CPU on it.
WiFi/Flash/USB/LCD Interface Board Resources