if you did an "auto" install of kali i.e use whole drive then as sam444 says it would have wiped your drive and for all intents and purposes kali has wiped it, it just didn't get to the point on putting itself on the drive. now if you went for a manual or they might called it "advanced" install you would have been able to choose where the kali was going and still leave other installed OS intact
A live distro is handy for quite a few purposes. For instance it would be nice to have screen shot of what gParted is now showing for your hd and if there;s any reminents that might be rescued.
So Mint or even kali live could help with that.
The basics of using a live Os from a usb is that you can via chroot evoke commands as if your OS on your laptop.pc was booted up and alive. So for instance you can re-install grub for the OS on a PC/laptop , from a OS running from a usb stick. It involves using the liveOS from the usb stick to mount your partitons and then using chroot, its as if you had the pc OS
up and running and were using commands from a terminal from your running OS on your laptop. Hope that makes some sense