6/5 Means that you can read at 6 metres what someone with 'normal' vision can only read at 5 metres.
The definition of 'normal' (6/6) vision is somewhat arbitary.
Anyone with no significant refraction errors, or corrected refraction errors, should do better than 6/6 on a good day.
If the second number is higher than the first your eyesight is imperfect. 6/9, otherwise expressed as 20/40 is the limit for driving in some US states and is not a problem for most purposes.
Anything better than 6/5 is very good, anything worse than 6/9 means you certainly need glasses.