Prove that if n is an odd positive integer, then n^2 ≡ 1 (mod 8)

also

Show that if n|m, where n and m are positive integers greater than 1, and if a ≡ b (mod m), where a and b are integers, then a ≡ b (mod n)

Just started doing congruencies. I understand mod no problem, but I am really lost when it comes to congruencies. Any help would be great.

Thanks