If you want to install Ubuntu in the free space on the HDD, you should first create a new swap partition in the free space you made on the HDD - Most people recommend making the swap the same size as your RAM.
Then, create a new ext4 partition in the rest of the free space, and use that for /
. (If you want a separate /home
partition for user data, you need to create two ext4 partitions - one for /
and one for /home
- you probably don't need that unless you want to install multiple linux distributions).
For the bootloader - you should choose the device from which your computer is booting, most likeley the SSD (You can check this under "boot priority" in the BIOS / Set-up).
Note that it's a good idea to always have a backup anyway, even just in case of possible hardware failure. If you want to be entirely sure, you can unplug or remove the SSD while installing, so nothing goes wrong even if you make a mistake, and then run update-grub
or grub-install
(or by using a tool like Boot-repair) from ubuntu to set up the dual boot menu after installing and re-adding the ssd.