Storage spaces is a new software alternatives to multiple-drive arrays such as RAID (in all its flavors).
This feature allows you to take any empty drives you have and combine them into one single, multi-drive, spanning array with either mirrored, parity, or non-redundant functionality.
Think of it as either RAID 1,5 or JBOD but you can use drives of differing size, can expand the array as new drives are installed, and the entire array can be moved as one Into any windows 8/server2012 machine with no data loss.
I am currently working on creating a new 25tb+ storage array with this. It's a great new feature and blows intels software raid solutions out of the water.
For a quick and easy guide for setting up a storage space, and what all the options mean, use this guide.
Any storage volume that windows can normally assign a drive letter to is eligible to be included in a storage space. Bootable drives are out though