The service set identifier is the name of your wireless network, allowing you to differentiate it from other networks in the area. The easiest way to find your SSID is to look on your wireless router. The default SSID -- the one it came configured with from the factory -- is always located on the bottom or rear of the router. If the SSID has been changed from the default or if you don't have physical access to the wireless router, you can find the SSID from a Windows 7 computer with Wi-Fi support.
Click the Network icon -- it looks like a row of vertical bars -- in the taskbar's Notifications area.
Find the network you are connected to at the top of the list.
Hover your mouse pointer over it to see information about the network settings, including the SSID.
If you want to connect to a network with a "hidden SSID" -- one that's not being broadcast -- you need to ask the owner of the network for the SSID so that you can manually connect to it. Give the SSID to your friends or colleagues who want to access your wireless network. If your network is secured, you need to give them the password as well.