@Peer I assume your computer is booting on the drive with ubuntu installed on it.
Try to change the boot order, and boot on the other disk. You should have the "debian grub".
You can also regenerate a configuration file for one of the 2 grub, and use it to boot either on Debian or on Ubuntu.
You dont really mind the format, you will need to create partitions anyway.
Why do you want to use it as a bare metal os and not a Vm ?
CentOs is by default a bit more server oriented than Fedora, and you will have access to all the features trough the vm without to have to part your Hard drive.
Bios and Bootloader are 2 differents things.
Your bios (Basic Input Output System) is basically a primitive level. He can detect disks, and performs somes really basic tasks on the hardware.
Your bios will detect the drives connected to your motherboard, and then access to the MBR (Master Boot...
Hello, and welcome to linux.org.
What you can try is to use a file manager (such as nautilus) to see if you can still access your datas.
Just to let you know, kali is not a made to be run as a main os, only for pentest/security.
No problem, ping me if you need :) You will see, if you really want to go minimalist and well configured, you can easily have multiple terms, browser with several tabs open, for only 750 Mb of ram in total :)
The man is a really good place to start.
If you want more guides than the manual you can use thoses ones :
Intersting for gapps => Install i3 WM in Arch Linux based Distribution
Intersting for the basic configuration =>...