I was under the assumtion that you could plant an apple seed and it would produce the same quality apples that the seed came from.

==>> this is wrong ... maybe.. maybe not.. the genetics involved seems to indicate the odds are very low ..

but your seedling could be used as understock.. if you got a piece of a good PROVEN apple ..

ken

Just like our children are different from us, your seedling is different from it's parents. (Notice the "s" in "parents". It is intentional. Most apples require 2 different varieties for pollination) Unfortunately the chances of your seedling having good quality apples is very very low. Additionally, your seedling will grow to be a very large (full size) tree and take many years to produce fruit. This is why apple trees are usually propagated by grafting: Identical fruit, control over the size of the tree (depends on rootstock), and dwarf/semi dwarf trees produce fruit much sooner.
As for doing the grafting, that's a whole other subject. There are a lot of great videos on YouTube that might be helpful. Search under "Apple grafting" to get started.
-Glenn