layering

me and my father r opening a nursery witch is grate for me i will have all the ferts and things i need at hand and iv been reading up on growing other kinds of plants and i came upon something called layering its when u take a branch lower to the ground and give it a little cup put some rooting powder on it and berry it what would this do for a plant like pot im curious to try it also douse any one know is it conseterd a tree or a shrub