Show from certain categories in multiple loops

I’ve been looking all over for this and keep coming up with the wrong results.

I need to make multiple loops so I can show all posts from a certain loop in each one. All the stuff I’ve found about this has only led to excluding categories, number of posts, which is the opposite of what I’m trying to do.

Basically I don’t want people to have to go to a separate category page to view posts and I need to separate them by categories.

This seems like such a basic function, maybe that’s why I can’t find any help on it. I’m sure people have done this before. Any advice?

In addition, I want to make each of these loops a dropdown, which I can manage by making a separate loop for each (if I can figure how to make separate loops). If anyone knows a way to do this using one loop and maybe javascript to select a category by rollover that changes the dropdown loop results that would be even more help.