겠어요 = will do something I will kill you = 난 널 죽이'겠어요'. 았어요 = the past form of a korean verb. I was very happy = 난 매우 좋'았어요' and 겠어요, 았어요 is kind of honorfic, so you can use it without '요' like this 난 널 죽이겠어 or 난 매우 좋았어.