I want to buy a Samsung Series 5 laptop, but I read, that an installation of Ubuntu could break it (because of UEFI). But I also read, that Ubuntu fixed the Problem. Is that right? can I install Ubuntu on it, without the risk to kill it?
You didn't post your exact model, but the problem is Samsung's, not Ubuntu's. Samsung didn't follow the UEFI spec and underconfigured the NVRAM -- you can brick those PCs installing another copy of Windows. Do all your research first to confirm any particular model will work with Ubuntu before buying. That said, if someone already owns a Samsung with a problem, and it cannot be returned to the vendor, I think setting up an EFI boot from a USB device, to boot a copy of Ubuntu on the hard disk MAY avoid adding to the NVRAM variables. You'd need to make space on the hard disk, do the Ubuntu install without a boot loader, and manually set up the USB stick to boot first, and have the stick's /EFI/Boot/bootx64.efi be the copy of shim, with the signed copy of grubx64.efi also in /EFI/Boot. Put grub.cfg into /EFI/ubuntu on the stick, and have it set up to boot the hard disk. Chancy, but I think that would not alter any NVRAM variables. Not recommended for a beginner.