The free space can found effectively as home directory, this can do it editing the fstab
file, which found into /etc
directory.
So you should open the fstab
file (as superuser, of course) and add the follow line to end of file:
/dev/sdaX /home ext4 nodev,nosuid 0 2
Of course you have to rempace the X with the correct number of your future home partition.
Once this is done, just reboot your computer. :)