Every ordered tuple picking one element from each set — A × B (or more sets at once).
The Cartesian product A × B is the set of every ordered pair (a, b) where a comes from A and b comes from B. With three or more sets, it's every ordered tuple picking one element from each set.
|A × B × …| = |A| × |B| × … — multiply the sizes of all the sets together. Two sets of size 3 and 2 produce 6 tuples; adding a third set of size 2 gives 12.
No — only the order the SETS are listed in matters (A × B is different from B × A unless A = B). Within a single set, duplicate entries are removed but the remaining order doesn't change the result.