Custom Post Types in the WordPress Navigation Menu

Hello can someone help me out by pointing me in the right direction as to where I can find out how to add a drop down menu to a theme with my custom post types stored within in, have been looking/searching google for “custom post types in wp_nav_menu”, “custom post types in wp_list_pages”, “custom post types in wordpress themes”, “custom post types in wordpress theme”, and have drawn a blank so far, I have managed to find out how to get my posts in the custom post types to appear in with the normal blog posts, but as I will have several posts in the custom post types more than what would be in the normal blog, would make this diluted and I would therefore like to have them in a drop down box in the menu.

The menu on this website here https://justintadlock.com/ the “Writing” part on the menu I presume that these are custom post types, but I wish to have the menu on my site like this menu, if anyone can point me in the right direction as to how to achieve this, be is something on the codex, a blog post or something like this I would very much appreciate anything anyone would be able to tell me.