To play Kayn first you will need to make pathing red buff,krugs,raptors, wolves you can smited early and you go blue buff and gromp and that's it for full clear before 3:15 and you'll need to gank if you want it too for orbs. Kayn has 2 forms that is Rhaast the red form and Shadow Assassin is the blue form. Melee champs will give you red orbs for your red form and ranged champs will give you blue orbs for your blue form.
If they have more melee champs you go Rhaast and if they have ranged champs you can go Blue Kayn.