"Random" means by chance, with no pattern (aleatório). The digits of pi are random: 3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5. Notice that the digits are random even though "1" appears twice, and 5 appears three times. If you flip a coin, heads and tails come up randomly. If you roll a die, the numbers 1, 2, 3, 4, 5, and 6 turn up randomly.
You "shuffle" a deck of cards to put them into a random order. After you shuffle them, there will still be four aces, four 2's, four 3's ... four queens, four kings, but their order is now random. By extension, "shuffling" can mean anything thing puts at set of objects into a random order.