(a) Prove that $N \times N$ is a countable set
(b) Let T be the set of two element subsets of N. Prove that T is countable.
This is a question in my exam review package. I missed the lesson on countable sets and such, proving them seems simple enough (I have what seems to be a decent solution package provided to me by peers), however this question is just all over the place in terms of an explanation.
I'm just wondering if someone could guide me through the explanation of the solution.