If your child is moving to Reception in September they will be developing an awareness of sounds and hopefully enjoy rhyming activities and will be developing an awareness of rhyme, perhaps being able to recognise rhyming pairs.
They should be encouraged to hear the sounds in words such as 's' for sun, as well as recognise pairs or groups of words which begin with the same sound.
As their awareness of sounds increases they will begin to be able to put sounds together to make a word. This can be either
-blending (putting sounds together to make a word) - if you say c-a-t, they can put the sounds together to say cat.
-segmenting (splitting up the sounds in a word) - if you say cat, they can say c-a-t
These are really tricky skills to master and it takes lots and lots and lots of practice for the children to become confident, so please don't worry if your child doesn't pick this up quickly.