查找关系的候选键,如果它是2nf或3nf

I am having issues with my homework. My teacher did not teach me well at all and I really want to learn how to do these problems. I am not asking for an answer, I am just asking for someone to point me to a website or question on here that will help me answer my own question. Here is the question that I have.

A relation R{A, B, C, D, E, F } satisfies the following FDs: 
AB → CD CD → EF 
(a)  What is a candidate key of the relation R? 
AB is a candidate key of the relation
(b)  Is the relation R in 2NF? Why or why not? 
Yes it is in 2NF,  all of the relations satisfy each other.
(c)  Is the relation R in 3NF? Why or why not
(d)  Is the relation R in BCNF? Why or why not? 

Now what I have found online I should break down the FDs into AB→C AB → D CD → E CD → F, but I really don't know where to go from here. I know a candidate key is something that can access all of the attributes, so I am assuming a candidate key for this question would be AB. I don't know how to figure out if it is in 2NF or not. Once again if someone could just point me towards something that would help me. I am not asking for the answer.