To say it concisely, a LOT.
The longer story is more complicated.
First, today, I saw this eyeopener (which, I'd bet $10 that MOST Americans also don't know):
Yes, my jaw really did drop at that (to me) news.
Nah. That would be CRAZY.
It's been a long time since I fired a gun. The last time, it was a .22 rifle of my Dad's. My brother had received it for his 12th birthday, and my Dad took him, and me, out to show him how to use it.
It was at an outdoor shooting range (the old kind, with haystacks in a field). The paper targets were fixed directly to the haystacks, and you had to wait until the guy in charge called "Clear" to retrieve them.
My brother shot some, I got some time in, and when we were done, we had an experience to tell our Mom and friends.
My brother was fine for a first experience - he probably needed glasses by then, but hadn't been checked in a while. So his scores were OK but not that exceptional.
Mine, on the other hand, were pretty good, for a 1st-timer. So much so, that my mother arbitrarily decreed that my shooting days were over. I sulked for days.
Her concern was for my brother's self-esteem - being outdone by a 2 years younger sister might be demoralizing. And, it is true, that I was a horrible braggart and lorded such things over him.
Later, in the Army, he had better instruction (my Dad was an excellent shot, but an impatient and lousy teacher). He also had free ammo and lots of time to improve. He eventually received a sharpshooters recognition.
If you want a fun but silly way to improve your knowledge of guns, try the Fieldstripping app - Weapon Field Strip 3D. I've played around with it, and it allows you to see how the various types of guns are put together. Also familiarizes you with the names of the parts, for the newb. Might come in handy for training those new to the discipline.