A player, after being dealt his first two cards, is always given the option to double the initial wager. Your hand will only consist of 3 cards. You would now be playing 2 separate hands, each starting with one of the two split cards. You will now be dealt a second card to one of the hands. After this hand is played out, the second hand will be dealt a second card and continued until that hand is played out.
All regular rules apply to each hand with the ability to double down.
You may only split your hand once and a new wager equal to the initial wager will be placed for each split hand. If the dealer's first card is an Ace, there is a possibility that he may have a Black Jack. The player can, if he believes the bank's hidden card is a 10, insure himself against Black Jack. If you choose to insure yourself you have to pay an amount of half of your stake. If the dealer gets Black Jack, the insurance will pay 2 to 1 which corresponds to your original stake.