What is an All-In and when should it be used in poker?

All-in is the act of wagering all of one’s chips. It is possible to go all-in during all betting rounds, including before the flop. All-in is used in the following No-Limit Holdem situations:
You have obtained a “premium” hand. Turn and River are the best rounds to go all-in, as opponents are more likely to call your bets at later stages of the game.
You hold a strong hand. If you are confident that your hand will produce a good combination on the flip, it is prudent to boost the stakes. If the opponent calls with extreme aggression, it would be prudent to go all-in.
You are holding poor cards and wish to bluff. In the movies, going all-in with a poor hand is a common occurrence, but you should avoid doing so until absolutely necessary.
You have the largest stack of all the competitors in the event. Your opponents with lesser stacks will do everything to remain in the tournament, so you go all-in and add the blinds and ante to your stack. Players with large stacks tend to play more aggressively than those with lesser stacks.
Nonetheless, your opponents may also go all-in. In this situation, the best course of action is to simply examine your cards; if you have a good hand, you may comfortably call, while those with weak hands should fold. If many players go all-in, the stack is divided according to the amount of large blinds each player has and the strength of their hand.