Prune or not to prune

Read a book today about apple tree growing - Didn't know 'Orchardeering' was a word! Also didn't know that the science of apple growing is called 'pomology'. Brilliant! 

Must be very careful about pruning these trees. Takes 3 years to do it properly. get it wrong and we could prevent fruiting for at least 3 years :( 

Need to read more about it. Need to make a plan.