There are people far more capable on here that will give you the answer you seek. For now I will tell you that I had the same problem you are having. Success sharing folders was hit or miss. All the while not sure of what I was doing. Even if it did work I wondered if I was making my machine less secure.
That all changed when I purchase Network Magic by Cisco (Pure Networks). As one of the feature it offer one button click to share folders or drives. Cool thing is it also gives you a graphical representation of your network.
They offer a 30-day trial. If all else fails download, run the trial, share your folders and uninstall. The folder sharing stays. I normally would not buy a utility like this but it was that useful.
.
