This dongle uses RTL8188CUS chipset, which has built-in support on the raspberrypi linux kernel. So it just worked after I plugged it to raspberrypi.
The next step is to configure the dongle so that it can connect to my wifi router. There is GUI based connection manager if you're using raspbian system image. But in my case, I use a small system image built with built from builtroot with only command line interface, I have to setup manually.
I enabled wireless tools in buildroot config, which provides tools such as iwlist, iwconfig. My wifi router, which is configured with dhcp server enabled, doesn't required password to connect. So I can setup the network with commands below:
Having tested the network run ok, I updated the /etc/network/interfaces file so that network would be setup automatically.
ifconfig wlan0 up iwconfig wlan0 essid WIFI_ESSID udhcpc -i wlan0
I struggled a lot with the interfaces file due to the dhcp always failed to work. And I finally found that the connman package caused the conflict. Disable it solved the problem.
auto lo iface lo inet loopback auto eth0 iface eth0 inet dhcp auto wlan0 iface wlan0 inet dhcp pre-up ifconfig $IFACE up pre-up iwconfig $IFACE essid WIFI_ESSID down ifconfig $IFACE down