New to the Game, What do you suggest?

i'm iron4 and i play mostly jungle because its more fun than others. But whenever i lock sonerhing but Kha'zix my game starts to go worst that you can imagine. Like 0/15/3 or 2/19/5... So what do you guys suggest? Where can i learn jungle or what should i pick? Where can i find builds with reasons (so i can learn items)?