You can create an ext4 partition on the whole SSD using GParted, and on the HDD: at the end a swap partition that is just a bit bigger than your amount of RAM, and an ext4 partition on the rest of the HDD.
After creating partitions, in the installer, you can use them this way: double-click the partition on the SSD, and select / as mount point, then double-click the ext4 partition on the HDD and set /home as mount point.
At the bootloader, you should select your SSD (and not any partition on it), so /dev/sda or /dev/sdb (whichever is your SSD) instead of things like /dev/sda1.
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