Actually, this is a complicated question. How DO you learn to handle a variety of guns?
Let's cover a wide range here; handguns, rifles, shotguns, carbines, SMGs... There are not many options for anyone to really learn about all of these.
1) Join the Armed Forces.
2) Join the Police forces.
3) Join a gun club where at least some members who have licenses that are rare hang out.
4) Ask to try anything you see.
When one of those options is picked; practice a LOT. Reading only means so much. You'd scream or die laughing if I showed you all the folks I've ever seen come to a real range with tons of "book-knowledge". They universally sucked.
At the other extreme, one of my best students was a young woman who had never touched a gun in her life. She started with no useless luggage and ideas, and was shooting at 80%-plus within a month. That's above the requirements for police officers by the way.