Lee, first, sorry for the wrong information about the license scheme. Thanks Pavel for correction.
To share a single folder just do the same you did to share the whole disk…
You should have gone to C:\ (root directory), right click, choose properties or sharing settings… Now you have only to go to an specific directory (not the root) and do the same. This way you will prevent the share the whole disk but just a part of it, a specific folder of your choice 