>>510365
>How long do firefights last?
Usually? Seconds. It's pretty rare that both sides are aware of each other before the shooting starts and are using cover. There are exceptions, but not a ton.
>How lethal are they?
Considering that very small pieces of metal are flying around at speeds that tear through the human body, pretty lethal.
>What are the most important components to winning a firefight?
Overwhelming your enemy via surprise, aggression, and volume of accurate fire.
>When is full auto used?
Do some reading. There are a lot of ways to employ automatic fire, with submachine guns, machine guns, automatic rifles, automatic grenade launchers, etc. The short answer is when a concentrated volume of fire is more important than the accuracy of individual shots.
If you want to learn about guns, make sure it's something you not only can afford to purchase, but something you can afford to shoot, even if it's a .22. Kill and clean some small game and you'll start to understand what bullets do to meat.