I learnt to read and spell through mastering phonics. Phonics is a series of rules that children have to apply when they are sounding out new words. Even as an adult, when I am unsure on how to spell or pronounce a certain word, I instinctively use my knowledge in phonics to sound out or to spell the word. Here's a website recommended by my friends where you can get free resources to teach your child reading via phonics:
http://www.readingbear.org/