Always talk to your child (about anything!), even when they don’t understand. The more words a child hears, the larger their vocabulary will eventually be – and that is very helpful in learning to read.
Not only that, but research says that children with a large vocabulary are better prepared for school.
This is another reason that it’s important to read to your child – you will give them about three times more new words than you would just by speaking to them. If they don’t understand a word, explain it to them rather than substituting a simpler word.