Effectively, in a first time I installed on my real computer the HDD, the correct software (TGT), and configurated it.
After, in my VM, I installed what they call “iSCSI initiator”, and configurated it.
After this two steps, in the virtual machine I was able to see my HDD with the command lsblk.
the last step was to simply mount it with fstab.
All this is correctly described in the link above.
There is two tutorial, one for ubuntu 18.04, and another for ubuntu 20.04