All children are different and read at different levels.
However for most 6 year old children the 6 year old child should be able to read around 20,000 words.
A 6 year old usually can read pretty good on their own but they still may have trouble pronouncing some words when reading.
It may take until around 7 or 8 years old before the child is reading really good on their own.
Some children may have a harder time reading than other children but it's a good idea to start reading to the child as early as 2 years old and sometimes sooner.
Reading is a good way to help the child learn words even if they are too young at the moment to learn to read it's still a good bonding experience and most children loved to be read too even if they may not understand what you're saying.
I used to hold my son in my lap as early as age 6 and read to him and he loved it and I continued to do so until he no longer wanted to sit in my lap.
Sometimes he still loved to sit in my lap at 8 years old and be read too and I used to read him bedtime stories and it helped him become a better reader as he aged and went to school.