If you don't have a store, you get 40 free listings at the start of each month and once you use these up you start getting charged listing fees.  Ebay of late have been granting random bonus free listings (usually 100-150 at a time for non store owners), but they generally have a limited shelf-life, 4-5 days only.  The links to these are received by some in emails, but are almost always posted here in the forums, so keep an eye out for them.  The last lot were a few days before the end of the month, but they expired last Sunday at midnight.  If you have used all your regular monthly free listings , that would be why you are being charged.

If you go to your My Ebay page and scroll right to the bottom, you should see any free listings you may have available spelled out for you.