I mean just install Debian to 2th SSD. And choose your OS with pressing F11 when your PC boots up. Can i do it like this?

You need to install a boot loader to boot your distro.
You don't need to install a bootloader with every distro - but in that case you can't choose from F11. Your choice.

So i need to install GRUB right?

With the F11 method you will need to install some sort of bootloader for each distro, whether it be grub or some other bootloader. The other option is to use one bootloader to boot both systems.

i use F2 or Del to boot up my box, it boots to windows 10 and i rather boot linux using bios settings, my computer illiterate friends are allowed to use just windows

When I dual boot I tend to remove the current drive that has a loader. Then install OS and return drive. While this usually works great to get a loader on each drive there are some cases where an update messes with the deal. I like to have a loader for each drive/OS but you don't "need" it. You do need to have a loader that can load the OS choice. Chain loading used to be very common.

You need to install grub in order to boot into Debian. The grub installer will ask you if you want it to find all of your operating systems. If you reply "yes" then every time you boot grub will give you a list of operating systems and allow you to pick the one you want to boot. There is a time out on the selection and grub will boot the first operating system on the list when it times out. After the install you can change grub control files to rearrange the boot order or change the time out time.

I have had as many as four operating systems on the grub menu.

You do not need a separate drive for each operating system, just separate partitions.