Dual boot - first time using UEFI

[Hans <hans.ullrich@loop.de>]

Hi folks, 

yesterday I installed debian bullseye besides a windows system. As UEFI could 
not switched off, I used gparted to make the windows partition smaller. 

Then used an usb-stick and installed bullseye as usual.

However, the installer discovered UEFI and respected this, but atthe first 
boot, only windows could still be booted. 

But the bios allowed me, to boot into windows again (using the F12 key) , and 
I could start the installed debian.

When I got it running, I tried to install grub again onto the MBR, which was 
successfull. But now appeared a blue screen, with choices: "Wait 10 seconds - 
go on - Restart - Do not ask any more" (similar, is from my remembers).

After choosing "Do not ask any more", the next reboot showed me the well known 
grub starting screen.

Well, everything is working, but the problem is: I have nothing learnt of 
this! 

Can ssomebody explain, what technically the grub installer did do? At one 
point it said "I have dicovered another EFI partition, shall I use it?" (or 
similar, it is from my remembers).

Thanky for making things clear.

Best 

Hans