DVD Extras - How do I "link" media together in Plex

Hi all,

Super new to Plex here. I've been looking in the help docs to figure out how to add "supporting media" to titles. I have a bunch of my films with DVD extras. How can I add these?

I thought this may help...
https://support.plex.tv/hc/en-us/articles/200264966-Naming-Stacked-or-Multi-Part-Movies

But this seems to be more for just split files across a single title rather than just separate linked media.

Thanks for any help.

Cheers