The way that the flu virus leads to death in most cases is that the flu leads to inflammation of the lungs which then leads to death.
You can have a more severe form of the flu and then get the inflammation of the lungs and then it makes it hard for you to breathe and when that happens you can die.
Also older people and younger people don't have really good immune systems and there immune systems can be weakened or weaker than other peoples immune system.
So that makes it harder for younger people and older people to fight off the flu infection.
Most cases of flu are just annoying and go away on their own within 1 to 2 weeks but if the flu gets worse or lasts longer than 2 weeks then you need to see a doctor or go to the emergency room.
If you're in doubt it doesn't hurt to get checked out at the emergency room just to be sure your virus is not very severe especially if you're older.
If you have a baby 1 year old and under and they have a flu it would be good to take them to urgent care or the emergency room especially if they have a 100 F fever and you cannot get it to go down or you cannot get them to take any fluids in.