FAQ (Correct) on installing Windows.

0)
First, save the data from drive C: (if needed).
Take the hard drive to a friend (if the system doesn't boot at all).
Etc.
And to avoid doing this... always store the most important data on other HDDs! Just not on C:

Here are some tips on "extracting" data from an already dead system, which would also be very useful, because this happens most often ;)

1) Turn on your computer and hold down the Delete key.
2) Enter the BIOS. (Insert the Windows disc into the drive).

This is one step. Pressing the key automatically initiates the process.
And also - on not all machines this key will be delete. Very often this role is played by the F2 key, and less often by ESC. Which one exactly is displayed during startup, during the POST procedure.

3) Use the arrow keys to move to the right to Boot.
4) When you reach Boot, press Enter, select BootDevicePriority, press Enter.
5) Leave only CDROM (this means that the boot will start from it).
Disable everything else. BIOS versions are different, but the principle is the same.

This is not necessary. Modern machines have a boot menu that can be called up, and you can already choose the device from which you want to boot. That is, it is not necessary to go into the BIOS. On most computers, this key may be F10 (most often), F12 or ESC. Again, which one is displayed in your case during POST.

8) Wait. After all operations, select the C: drive.
Only on drive C! (It will be 1 in the proposed ones).
9) Format it (for example, for Windows XP), this will be NTFS (Quick).
10) Confirm with the F key.
11) After formatting, the Windows installation will begin.

There isn't always a C drive) it may be that the machine is new, then you need to create partitions yourself. Formatting is not always necessary. Sometimes you can install the system without it.

Why go through all this? It is enough to set the desired CD-ROM in the First Boot Device field.

cd rom in First Boot device slows down the boot. The system hard drive should be there. Although slightly, but it slows down. This is if in one place it is insignificant. But there are a lot of such places in the working system ;) and if you minimize the time of the procedure in each of them, this will give a noticeable result in the overall operation of the system. And during boot, yes, an insignificant delay, especially if the boot occurs once a month at the worst times)) In general, I wrote above that you don't need to touch the boot priorities at all, because you need to use the boot menu.

Well, since that's the case, I need to post another useful recipe that I once found on the Internet...

There is also a tool called PE_to_USB, which is also designed to create a bootable flash drive with Must-Have. And a detailed manual for it is also available on the Internet, I will post it sometime later.

Dr Motorcd rom in First Boot device slows down the boot. The system hard drive should be there.

Nothing, absolutely nothing prevents you from putting it back after installation.
You are right, it doesn't prevent. But why put it there and back if you can not touch it at all? :D