The simple answer is, you do.
From the moment your child arrives in this world, you are his main contact with everything around him. Initially, you ensure that he is fed and clean, safe and warm. He - we'll call him "he" for the purposes of this discussion - learns from that. Your child learns from your voice that you are near, to be relied on, and will provide these essentials. A little later, he recognises your face, your touch and, increasingly, the variations in the tone of your voice. From you he learns about hot and cold, wet and dry, quiet and noise, light and dark.
If you think, for a moment, about the importance of these things you will start to see how crucial they are and that it is only through you that your child grasps an understanding of them.
Your child learns fast. He learns about hungry and thirsty, inside and outside, moving and stillness, home and everywhere else. He will learn other faces, other voices but yours will remain the trusted one - you feed him and he will be hungry for food - real food but also brain food.
It may not be exclusively you, of course. He may learn quickly that there are two or more such trusted voices and faces - your partner, your parent, a sibling, a friend or nanny.
But watch him - he will be looking at everything, wanting to touch, to taste, to observe. He will be busy learning that trees wave leaves over his head, that cats have soft fur, that food can be cold or warm, that voices can be loud or soft, that faces can be smiley or stern, that clothes can prickle or soothe, that baths are wet and that some things are very funny and make him laugh till he cries.
Suddenly you realise that he is understanding actual words. You say, "We're going out now" and he comes back trailing his outdoor clothes. You say "Granny's coming" and you find him looking out through the window. You can now ask him, "do you want more banana?" and if he shakes his head it's a fair bet that he doesn't!
All this time, whether consciously or not, you have been his teacher. From you he has learned all the basic concepts of life that he will use for the whole of the rest of his.
But your role has only just begun and it is now as important as it was the day he arrived.
All good parents want to help their child learn, achieve his potential, do well at school. But, all too often, they think this entails signing up him for umpteen classes, engaging tutors and frantically bundling him in and out of his buggy - or the car - getting him to all these activities. Everyone else does it so you must - or you're not being a good parent.
It's expensive, exhausting and - if you think about it - not always the best thing. Or not for each child, all the time.
What most children like best is time with their parents or primary carers. They like to chat, to share activities, to watch what you're doing, to experiment, to make things with you, to discuss things.
They learn more from this kind of thing than from any classes.
If you are a parent with a job then time for this kind of thing is limited. There may be a little time early in the morning, last thing at night, at weekends - and sometimes not even this amount of time. It's just the way life is.
Do not overestimate the value of cramming this time with a class or an activity, especially not when your child is young ie pre-school.
He will learn more from being with you - whether chatting at the bus stop or when chopping vegetables, putting away clean clothes, brushing the dog - than from anything else.
This is not because you are actively teaching him but because, in sharing this time with him, you are showing him that he is valued, that talking with him - hearing his questions, his opinions, his observations - matters. This will make him value himself, will make him eager to learn more to share with you, to test on you, to challenge himself.
It makes no difference if you are rich or poor. Whether you live in a flat, a house, a palace, a B & B. What matters is that you give that little bit of time that you have to your child.
If you are walking with him to school, talk to him not to your mobile. If you are travelling with her on the bus, talk to her rather than plug in your ear-phones. If you are out for a meal, don't hand him his ipad, talk to him.
There are always things to talk about. The people around you. The weather. School, family, friends, neighbours, news, plans. Stories you have shared. Programmes or games he's enjoying. Ask him his thoughts on this or that. Share yours with him. Ask him his opinions.
These things will give him confidence… A confident child challenges himself, has high expectations of himself, isn't afraid to ask.
And you will have taught him how.