To create custom menu in Moodle 3.0 follow below steps...

1. Go to Administration > Site administration > Appearance > Themes > Theme settings
2. Scroll down to 'Custom menu items' and enter menu name and hyperlink
   

Note: Write menu name, then Vertical bar ( | ) and url where you wanted to hyperlink

For more visit https://docs.moodle.org/29/en/Theme_settings#Custom_menu_items