To Make a Project Private:
If you'd like to make your project private (invisible to everyone but you), you can adjust this by going to: Edit Project --> Settings --> Project Visible To --> Edit.
To Make a Project Private, but visible to a few, select Specific Members
Note that on Behance, there is no way to make a project private, AND visible to anyone you send the link to. For more privacy options like password protected projects, consider using our portfolio service, Adobe Portfolio (myportfolio.com)