Look up the function Part. The double brackets below are a way of using Part.
data = Table[{i, j}, {i, 1, 7}, {j, 1, 4}]
(*
{{{1,1},{1,2},{1,3},{1,4}},{{2,1},{2,2},{2,3},{2,4}},{{3,1},{3,2},{3,\
3},{3,4}},{{4,1},{4,2},{4,3},{4,4}},{{5,1},{5,2},{5,3},{5,4}},{{6,1},{\
6,2},{6,3},{6,4}},{{7,1},{7,2},{7,3},{7,4}}}
*)
(* take rows 1, 3, 4 *)
data[[{1, 3, 4}]]
(*
{{{1,1},{1,2},{1,3},{1,4}},{{3,1},{3,2},{3,3},{3,4}},{{4,1},{4,2},{4,\
3},{4,4}}}
*)
