In this digital age you probably aren't familar with an analogue clock so your difficulty is quite understandable.

There are twelve evenly spaced numbers from 1 to 12. There is a big hand and a little hand. See analog clock - Google Image Search

At 8 o'clock the big hand points to the 12 and the little hand points to the 8.

So the hands subtend 1/3 of 360 degrees, that is, 1/3 of radians ......