Step 2 - Click on public_html

NOTE: If you want to only password protect a subdomain, subfolder or addon domain (eg: test.yourdomain.net.au or yourdomain.net.au/membersarea/ ) you can use this menu to navigate to that folder)

Step 3 - (1) Tick Password protect this directory (2) Enter a name for your reference (3) click Save

Now add a user and hit Save

That's all done!

Now when someone visits your site they will get this pop up before and content loads: