There are 6 time zones in North America. Atlantic Time Zone (ADT), Eastern Time Zone (EDT), Central Time Zone (CDT), Mountain Time Zone (MDT), Pacific Time Zone (PDT) and Alaska Time Zone (AKDT).
So when you are watching T.V., they will always give two times. The first one is the time at wich to T.V. show will be broadcasted locally. They give you a central time so that you can see at what time it will be played at your house since a lot of T.V. channels are broadcasted across north america. A T.V. show that is broadcasted at 12 o'clock eastern time will be played at 11 o'clock central time. If you live in the pacific time zone, it will be played at 9 o'clock. They write it 12/11C so that if you live in the pacific time zone, you can calculate that it will be played 2 hours before 11 o'clock for you.
Sometimes you will see something like 12/2C. This means that it is being broadcasted in the pacific time zone at 12 o'clock. So if you want to watch it in the eastern time zone it will be at 3 o'clock.
It is actually really easy to understand once you understand what is the difference in time from your home to the central time.
Example: I live in Quebec, Canada. This means that I have +1 hour on the central time zone. So If I see something say 8/7C I know that the "8" is actually for me. At the same time if it says 5/8C, I know that I have to add 1 hour to the central time. This means that it will be playing at 9 o'clock for me.
I hope it helps, good luck.