The smallest unit of an SSID is a Virtual AP profile. To add an SSID to an AP or a group of APs, you need to figure out which AP group you want to add the SSID to. When you find out, go to Configuration> Wireless> AP Configuration. Click on the AP group that you want to add the SSID to. Click on Wireless LAN. Click on Virtual AP. In the right pane, select the Virtual AP Profile (SSID) that you want to add, then click on Add. Click on the Apply button in the lower right hand corner.
Click on Save Configuration to make it permanent.
On the Monitoring Tab, click on WLAN to see all of the access points that your SSID is on.