Thanks for writing. The easiest way to grow the seeds of an apple is to find a corner of your garden this fall, loosen the soil, and amend it with compost. Then plant your seeds and mark the corner. In spring, they should germinate into baby apple trees.
One note: Because 'McIntosh' is a hybrid apple, the seeds will not grow into exactly the same kind of tree as its parent. There's no telling what kind of apples your new trees will produce -- some could be good and others could be low quality. It's really a roll of the dice. So if getting 'McIntosh' apples is important to you, I'd buy a 'McIntosh' tree.
---Justin, Senior Garden Editor, BHG.com