this build will allow you to kill you enemys fast but katarina's weakness
is that shes easy to be killed but she can run and kill really fast
and this build allows her to chase down her enemys and kill they because

While they are slowed you can use the ultimate on them and finish them
but if they run away try to dash to them and kill them but never stay
alone at the first 6 levels because your an easy kill stay with a tank

or a carry or someone that heals or protects your life so that you can
easily harras your enemys from a good range and make they recall so that
you can gain the control on your lane without any difficultiss

---I dont spell right some words xD