I would very soon like to buy a new notebook with a 1000 GB HDD and a 256 GB SSD. Now of course I want Windows 10 installed on the SSD to boot from there. Windows does that automatically or do I have to adjust the initial settings myself?
You have to specify this during installation.
If Windows is already preinstalled, then Windows is already installed on the SSD.
For most tow-tops, the operating system is already installed and, for the system to start very fast, on the SSD.
I would take the HDD as a storage medium.
Where do you have to enter that? Yes Windows 10 would be preinstalled. Can I check this later in the BIOS, if the SSD was used or should I rather check it on the drive itself?
You do not have to specify that.
In the BIOS you have to check nothing. Just let the notebook come, start it and open the Explorer.
If it is preinstalled, it is certainly on the SSD, then you do not have to do anything, if it has Free-DOS or Linux, you have to delete it and select the SSD during installation, but the SSD will be in the BIOS as 1. Drive specified, then Windows makes it automatically.