Free NAS is pretty powerful and you can do a lot with it. It's primary feature is the ZFS file system which is very good. I would suggest reading the knowledge base articles on FreeNas's website to understand how it works. One thing you may notice is that a lot of hard core FreeNas users can be very vocal about using ECC ram with FreeNas. IMHO, while ECC ram is probably a good idea (heck all computers should use it), it's very expensive and you pretty much need server/workstation grade parts to make use of it (ie: Xenon CPUs). That being said, you can run FreeNas with non-ecc ram, which is pretty much all the ram you can get for the majority of computers available and is much more affordable, compared to it's ECC counterpart.
The reason I suggest to read the knowledge base first and or watch some YouTube videos is that depending on what you want to do with it, and how much space you want, it will dictate how much ram you may need as the ZFS file system is highly dependent on ram.
It may take a little tinkering, but if you can swing it, FreeNas is a very good solution.