Make sure you're in the User Panel (click on
User Panel, and then click on the domain with the folder you want to
password-protect if you have multiple domains). Click on "Password
Protected Directories", and then click on "Find a Directory to Password
Protect". You should be placed in the domain's public_html folder.
Navigate to the exact folder you want to protect by clicking on the
folder names. If necessary, you can create the folder you want to
protect by typing the name next to "Create New Folder" and clicking
"Create".
Once you find the folder you want to protect, click Protect. Check the checkbox next to "Use Password Protection". Enter the prompt you want to provide users, the username and password you want to require users to enter. Pushing Save will cause the folder to be password-protected.