The 40 words and non-words are divided into two sections – one with simple word structures of three or four letters, and one with more complex word structures of five or six letters. The teacher administering the check with your child will give them a few practice words to read first – including some non-words – so they understand more about what they have to do. Each of the non-words is presented with a picture of a monster / alien, as if the word were their name (and so your child doesn't think the word is a mistake because it doesn't make sense!).
You can download the Department for Education's official Year 1 Phonics screening check past paper from 2012, 2013 and 2014 to get an idea of what your child will be asked to do.
Phonics screening websites
Phonics play (Obb and Bob)
Information about the phonics screening test
The Ruth Miskin Read Write Inc website may also be helpful with its range of information and videos.