Blending is the process of saying the individual sounds in a word the running them together to make the word. For instance sounding out d-o-g and making dog. It is a technique every child will need to learn, and it improves with practice.
To start with you should sound out the word and see if a child can hear it, giving the answer if necessary. Some children take longer than others to hear this. The sounds must be said quickly to hear the word. It is easier if the first sound is said slightly louder.