Blackjack Tips Information & Video Source:

When playing blackjack one of the most favorable situations comes when the player gets the chance to double down.

Players are allowed to double their bet after the first two cards are dealt. The player then receives one card only on his/her hand. While some casinos allow players to double down on any two cards, other casinos limit the double down only to hands that total ten or eleven.
Having the opportunity of doubling your bet increases your chances to hit a bigger prize and lowers the casino house advantage; however, players also take the risk of losing two bets if they double down when they shouldn’t.

In this free Blackjack video tutorial, players can learn the basic double down strategy and pick up when Doubling down can give you an edge over the house.

Source: YouTube