When children are making marks they are trying out new things to see what happens. The marks children make slowly begin to have meaning to them and you will be able to see this by listening to what they say when they are involved in their mark making.
Through making marks, children are developing hand - eye coordination and muscle control, both of which are needed for writing to progress at a later stage.
Remember to encourage and praise your child. You will be developing their sense of worth and self esteem. This pre- writing stage is hugely enjoyable and rewarding for children and should not be rushed in an effort to get a child to hold a pencil and write letters. Let them enjoy it and when they are ready the rest will follow!