Are you asking how to setup your FreeNAS so it looks like your old NAS and then moving over your files?
Setting up FreeNAS and shares, read the user manual, create a dataset and enable CIFS shares at a minimum.
I'd copy your files over (not move), you can't have too much data on that old NAS and if you don't know how to setup rsync, it's likely the quickest way to get it done.