Initially, you will require apple seeds to proceed any further. Just save some seeds when you eat an apple or you can simply buy some seeds from a store.
Put the apple seeds aside to get fully dry. You can place them in sunlight until no moisture is left in them.
Once the seeds are fully dried, cover them up with damp paper towels and make several folds to it. Place the folded paper towel in a refrigerator and wait until the seeds sprout. It will take about one month before they do so.
Take a small cup filled with moist potting soil and place the seed within it. Make sure to add some water to the soil but not too much quantity, otherwise the soil will dry up and crumble afterwards. You just have to wait until the seed grows a bit further.
Once you see some growth in the cup, transfer the newly sprouted seedling to a larger pot. Don’t forget to water the pot daily.
When you notice your apple plant has grown reasonably bigger for the pot to contain, it is time to plant it into the ground. Choose a suitable location, which is convenient, spacious and gets proper sunlight for healthy growth.
Carefully transfer the apple plant from the pot to the hole dug in the ground and try not to damage any roots. Your plant hole should be much larger than the roots. Add water and soil into the hole and spread hardwood chips in 3-foot circle around the plant. This will prevent grass from growing around it.
Since you are aiming to get purely natural apples, you better not add any synthetic fertilisers to your apple tree. Leaf mulch and compost can be used as natural fertilisation for your tree.
All you can do is wait and wait, until the apple tree grows sufficiently big to bear fruit.