The word 'List' is systemically reserved. (At least in version 11.3) You will see an error message if you use 'List' as a variable name.
So, let
Lit = {{{a, b, c}, {d, e, f}, {g, h, i}}, {{j, k, l}, {m, n, o}, {p, q, r}}}
Then my answer is
A) Lit[[1]] will produce {{a, b, c}, {d, e, f}, {g, h, i}}
B) List[[1]][[2]][[2]] will produce e
[[n]] means n-th object in the list.
And.. this is my first answer in stackexchange!