UMG layout rules ?

No, that’s not what I am wondering about.

I read docs, I watched WTF is? videos on youtube, so I got some ideas about UMG and widgets. However, none explain why use one over another widget and what’s the proper hierarchy. For example, WTF is? or HTF do I use ? videos imply that Canvas is the one that always has to be the parent. However in the video I linked he uses size box first, then canvas, then size box again.

Here is what I am after (that will be a 3D widget located in the lower left “corner” of the player’s view):

Basically a vertical box with semi-opaque background that houses several item widgets (initially there will be none, but as player picks up unique items, item widget with appropriate icon is added to the vertical box). On stacked items the amount (x999 text on the mockup) will change, on unique items it won’t even show.

I already have inventory system working. Now I just need to make UI for it :o