Some samples from Leonid Shifrin’s book.

(*complextestlist=Range[5 * #, 5 * #+ 4] &/@ Range[5]
Part[ complextestlist, All, 2]
complextestlist[[All, 2]]
*)

(*complextestlist = Range /@ Range[6]
plist = Position[ complextestlist, 4]
Most /@ plist
Map[Most, plist]
Most[plist]
plist[[All, 1]]
(* All the lists in complextestlist that have 4 in them *)
Extract[ complextestlist, Most /@ plist]*)

(*Clear[names, scores]
names = {"Joe", "Moe", "Ho"} ;
grades = {70, 80, 90};
{names, grades} // MatrixForm
{names, grades} // Transpose // MatrixForm
*)

(*list = {{1,2,3}, {2,3,4}, {3, 4, 5}}
list^2
Apply[ Plus,list^2 // Flatten ] //Sqrt
Plus @@ (list^2 // Flatten)
Plus @@ {1,2,3,4 , 5}*)

(* chapter 4, functions: downvalues with and without an argument parameter that collides with a global. *)
(*Clear[f, g, x]
g[x_] := x^2 ;
x = 5 ;
f[x_] = x^2 ;
(*ClearAttributes[#, Listable] &/@ {f, g} ;*)
SetAttributes[#, Listable] &/@ {f, g} ;
f[{1,2,3}]
g[{1,2,3}]
DownValues[f]
DownValues[g]*)