Indeed, why? What SSH even is? SSH stands for Secure SHell, but it actually has nothing to do with shells or cores. A ‘shell’ is just a name, traditionally used in computing to denote a way to ask a computer to perform exact tasks. That is, 90% of exact tasks are asking a computer to compute something. You know, that mode of your computer, when this huge 1000$ machine actually works as something it was designed to be 70 years ago: a huge calculator. (By inexact tasks I usually denote tasks which require automated, but not exactly computational tasks, such as calling your friends by a voice chat. )
When you use your calculator, you don’t really need any specific introduction into typing numbers, do you? Well, as I said, a personal computer is a very huge, and a very advanced calculator, so it needs a special advanced program to ask you for your formulae.
The word Secure here implies that using SSH, you can actually ask other computers to be the calculators you ask to compute something for you, and those only need to have the SSH on them, and be connected to a computer network.
So the main task of SSH is establishing connections to other calculators.
Is it so hard? Why would anyone have an extensive manual for a program which performs such a simple task?
There are many answers, but the main one is: not being obvious. The hardest thing to get used to when working with computers is that they are actually one of the least obvious things you find in this world, even less obvious than people.
It doesn’t mean that they are hard. Quite on the opposite, since computers are very dumb, and quite fast, if a good manual is available, few things are actually easier than computers.
But computers are painfully unobvious. Which image among the ones you see on your screen is a real one, and which one is a compressed one? No way to tell. Is the password you are typing on a website stored somewhere or is it not? Are you being attacked by hackers right at this moment, when you are reading this?
The answer to the last question is ‘yes’, even if you are not even remotely aware of the existence of those hackers. And they are also not even remotely aware about your existence, but they don’t even need to. They have robots do all the dirty work for them.
And this is also the place where official manuals fail to increase the obviousness of what is going on, as they are bound to only describing what a program should do, but not what the program should NOT do.