The Ace will always e considered an 11 by default. However, if you have a hand that equals 11 or is higher to it, then the ace will be considered a 1. It's a simple concept: the ace will always be an 11 unless your hand would surpass 21. If you have a hand value of 10 or lower without counting the ace, then the ace will be worth 11.
Keep in mind that the rules regarding the value of the ace are the same both for the player and the casino, which means that you might be tempted to buy insurance whenever the dealer reveals an ace. The situations in which it's worth buying insurance are so little that we often recommend to our readers not to buy it under any circumstances.
Even if you see that the dealer has an ace, do not spend extra cash to insure yourself. It's better to take the risk (odds of the dealer having another letter or a 10 aren't too low, but there's still an 11.65% chance of the dealer busting in that hand). You can play blackjack and test your luck using the best blackjack strategies and blackjack no deposit bonuses in one of the best blackjack casinos, which can be found here: