you should tell me where should I write it
There are two options:
1. You can run it from console window, if you are in the folder, where you have your Bitcoin application.
2. You can just append those options in the Properties, as you already did.
So, you did the second thing, and I assume it is correct. The reason, why it doesn't work, is that you had before some other settings, which may not work with what you are trying to do now.
Which means, that the way forward is not about changing the command, it is about cleaning up your wallet directory (if you want to use signet).
But: you can use "bitcoin-qt.exe -regtest" in the Properties window instead, and see if you can run regtest correctly. Then, at least you could mine some blocks locally, and test some basic things, without worrying about downloading the chain.
I don't know if it's a command line or something.
It is a command line. But guess what: putting those commands in the Properties, leads you to the same results, as you would have, if you would put it in the console.
For that reason, if you would use "notepad.exe" instead of "bitcoin-qt.exe", then guess what: it would open a Notepad instead! There is nothing fancy here, just a command to run your application.
How do I suppose to learn these things?
Well, it is not about Bitcoin. It is about knowing, how programs are executed by Operating Systems (Windows in this case). Which means, that if you want to learn such things, then it is completely separated from learning about Bitcoin, because if you would want to run Notepad or any other program, and modify the command line options, then those steps would be similar.
There are no youtube videos for these guides.
Of course there are. For example, here is some video for Linux:
https://www.youtube.com/watch?v=o-NYviYuUVMAnd the first comment: "I like how you started with the result instead of the boring part of downloading the files, etc."
So, I guess for different people, there are different needs. For some people, it is obvious, how programs are executed, and for some others, click-by-click explanation is needed. If you are in the second group, then you can get more knowledge not only by looking at Bitcoin-related tutorials specifically, but for example by also learning, how shortcuts in Windows works. And that kind of knowledge is a different matter than learning about Bitcoin, it is rather learning about your Operating System.