The rootstock mearly dictates the eventual size or cold hardiness of the tree, for example an m26 rootstock will give you a medium sized tree up to 3m tall.
An apple tree will be what ever variety you choose to grow, grafting your plant onto a rootstock means that you can choose how big you want the tree to grow or how cold hardy you need it to be.
If you take a cutting above the graft union it will be an exact clone of the parent plant.
For a full explanation of how rootstocks benefit the grower follow the link.
A cutting, be it a soft wood, semi ripe or hard wood cutting will always be a clone of the parent.