It's only possible to add password protection to sub folder in albums uploaded to jalbum.net.
Open the album you want to add password protection to and then go to Upload/Manage.
Make sure your jalbum account is selected as account profile and press Connect.
When you are connected to the server you are ready to start adding passwords, but if the album is not uploaded yet, that needs to be done first. Just press the Upload-button.
Click on the small arrow to show all album's the sub folders.
Mark the sub folder that you want to add password protection to and click on the password protection-button in the tool bar.
Enter a password and press OK.
Do the same for all folder you want to add password protection to.
Just press Close to close the connection and open your online album in a browser. When you try to open the sub folders in the album it should look like this: