I'm going to throw something else in there, which is 을\를. 을\를 and 이/가 are subject and object. So, 을 verbs the 가. Does that make sense? In Korean, the order is, "object-을 subject-가 해요." 을 normally comes first! It's actually really useful because in English, we don't distinguish so clearly what the subject and object are. It's all done by word order and implication. 는 is a bit more special. It's called the topic marker. If you want to stress what you're talking about, you can throw it in there. It can be sort of translated as 'as for', so when you read '저는', it's like saying, 'as for me, such and such a thing.' 는 does actually have another use, when you find it with verbs. It's like '-ing' in English.

I guess this is one of FAQ of Korean. Refer to my answer in http://www.italki.com/question/250760 See also http://www.italki.com/question/250570