If you are already connected to a network:
Windows XP: Move your mouse over the little computer with 'waves' coming off of it in the lower-right hand corner of your screen, and you will see something like "Wireless Network Connection (XXXXXXXX)", where XXXXXXXX is your SSID.
Windows Vista / 7: Click the "bars" (like a cellphone signal), and you will see "Currently Connected to:" with the SSID afterwards.
Windows 8: Move your mouse to the top or bottom-right corners (or swipe from the right on a touch screen), and choose "Settings" (gear). The SSID is displayed under the icon that displays either a computer or a set of bars (similar to a cellphone).
Mac OS X: Press the Airport icon at the top-right of your screen (series of waves/curves spreading upward). The SSID is displayed beside the check/tick mark.
- If You Are NOT Connected to the Internet ***
Personal/Home: Check your wireless router(box) for the SSID and password(if applicable), which could be labeled on the bottom or side of it. Or, check another device that is already connected by following the steps above on a computer that has a connection.
Business/Public: Ask the staff or management for the information, and thy will provide it if they allow you to have access. Many restaurants have a simple-named SSID that is easy to find within a list. Just be sure to take care when you connect in a public place, and avoid doing any personal business over these connections without a form of encryption (security).