Firefox bookmarks

This is likely a basic question but it's driving me nuts.

I'm using FF 45.0.1.

I can't figure out how to put a new bookmark into an existing bookmark category.

For example I have category or directory of bookmarks for XYZ subject and I want to add a new bookmark to this specific category.

The only way I can figure to add a bookmark is to click the star symbol to the left of the bookmark symbol on the menu bar at the top of the screen (whatever that's called these days).

Of course when you do this it just dumps the bookmark into the unsorted bookmark area, so now I have a list of 'unsorted bookmarks' that need to be put in the right category.

I have two questions.

1) when I come across a website that I want to bookmark into a directory/category that is already established, how do I put that bookmark directly into said directory from the get-go.

2) I have bookmarks in the 'unsorted bookmark' area that I need to move to their proper directories, how do I do that?

It used to be pretty intuitive to do this in firefox but over the years the "improvements" continue to happen...

Thanks