EAsy question -- hope you had it answered if not, here goes.
- Open the folder you want to share.
- Go to 'Tools' > 'Folder Options'
- Go to the 'View' tab and under advanced settings scroll down and make sure 'Use simple-file sharing' is unchecked. Uncheck it if you need to, then hit OK.
- Right-click on the folder you want to share.
- Click on the 'Security' tab.
Give 'Everyone' full control on this folder, but nothing else. Then create a user with a password that can access this folder. Give that username and password to anyone who you would want to access the folder.
If your folder is small and not with a lot of documents, convert the folder to a compressed/zipped folder, and add a password.