Is windows installed automatically?

I want to buy a laptop soon and i would like to know if windows is already installed or if you have to buy something. If so, how do you install windows?

Windows is often preinstalled. But that's also there.

Otherwise just look for how to install it on YouTube or on the Microsoft site.

You have to take from the description. Usually it is on it, but there are also some where only Free-DOS is on it.
Installation is quite simple, you just have to follow the instructions. You either need a DVD or a USB stick, which you can make or buy beforehand.