Free usage is when there is no charge just to have the use of something. There might be costs involved in obtaining the item (e.g. for free usage of software, you still need some way of copying the software, such as a network connection or a physical medium, and these may cost something to obtain, but there is no charge for the software itself).
Note that a thing may be free in this sense while still being encumbered in other senses. For example, you might have been given a free knit pattern (instructions for knitting a particular item), but that may not give you the right to sell items you make from that pattern.
Possibly there is a better word than "free" for this usage; I just can't think of it at the moment. "Uncharged" sounds like it could mean something else; "zero-cost" is wrong, "zero price" might work but sounds awkward; "unpaid" implies the possibility of "stolen"...