Players' cards are dealt face up with the dealer's first card face up and the second face down. The former is know as the up card with the latter referred to as the hole card. Now is the first variation of the rules with US casinos checking for blackjack if the dealer's up card has a score of 10 or higher. If the dealer does have a blackjack then they will collect all losing bets immediately and there will be a push with any player that has a blackjack themselves. Other casinos will not check for blackjack first.
Insurance is one form of side bet offered when the dealer's up card is an ace.
Each player is given the chance to accept insurance and pays 2 to 1 if the dealer has blackjack. The general advice is to avoid the insurance bet except in very limited situations. To accept it simply place chips equal to half your original bet on the area of the table marked for insurance. If the player doesn't require any more cards they will stand. For the benefit of the dealer and the surveillance equipment the signal if you wish to stand is to wave your hand away from yourself and towards the dealer.