Note: This feature is only available to ArtStation Pro members.
You can password protect pages on your ArtStation website. On the Website Builder > Pages, create or edit a page, and on the right panel there is a password box. Once you have set a password, visitors to that page will be prompted for a password.
Only the page is password protected - assets/images on the page cannot be password protected or locked down. If you are looking for protection at the asset level (i.e. images should not be accessible by the public at all, even if they know the URL), it is beyond the scope of most website builders and you should use a file-sharing tool such as Dropbox or Google Drive which is purpose-built for that.
Projects/Artwork/Albums that are included as galleries on the page are not password protected. This is because artworks and albums act as links out and are not on the page itself. Password protection will only protect the page itself.
Links from the page are not password protected. e.g. if you link to another page, or projects on your website, those are not password protected.