Now that A, B. = 이제 A 했으니까, B. ex) Now that I brought a cable, let's try to connect it to the machine. = 이제 연결선을 사왔으니까, 그 기계에 연결해 보자.

-니까 = Because/So 그사람이 착하니까 제가 좋아해요. Because that person is nice, I like him. / That person is nice, so I like him. It's used this way in both formal and casual speech.

-니까 (nikka) i think thats a formal way of ending sentences..

니가 (ni-ga) is a very casual way of saying you heard in songs a lot. However, 니까 (ni-ka) is actually a verb attachment. And Joh is correct. 니가 좋아해(요) (ni-ga joh-a-hae (yo) )is a way to sing/say "I like you". Thanks for commenting on my question!

Uh.. that's 니가 A.J. And it's 좋아, not 조하.