I would really leave this to the school (depending on the age) the school should run parent workshops and give out information packs when the time comes.
Each school will have chosen a phonics scheme to follow - so if you try at home you run the risk of causing more confusion by teaching it differently!
Essentially though, you teach 'pure, initial sounds' 'm- a- t- d-s' as pictures first (mountain, apple, tower etc.) until children can recognise that all pictures have a corresponding word that contains sounds. Then you move into the letter name and the sound that makes, eventually building up to recognising multiple letters/sounds and blending them to make words.
I'm a nursery teacher and I'd encourage my parents to orally blend words eg; 'oh let's put on our 'c-oa-t' and get our 'b-a-g'. The children have to be able to hear sounds before they even attempt to read.
Alongside lots of nursery rhymes, action songs and stories!
In reception/end of nursery they rehearse the sounds they know and begin to read these in very simple books. Each set of books contains specific sounds to practise. Once the children know the sounds they can segment/blend in new words, so they don't need to be explicitly taught every single word, only the sounds they contain.
There are lots of 'sound charts' online that show the order the sounds are taught (read, write inc is my favourite scheme.)
Sorry for the rant, I'm very nerdy and passionate about early reading 😂