Confused about context menus

I´ve been searching for a while and couldnt find an answer on how UE4 handles out of context menus, i understand that ther is a default HUD class that you can just add stuff in ther and it will always render on top of evrything but, how should one go about displaying a menu for a shop for exemple??

Imagine thers a map thats has the sole porpouse of being a shop and when the player enters said map a custom UI appears, handeling that kind of logic in the HUD class makes no sense.

The answer probably has something to do with widgets but i couldnt find a decnet explanation on that either.

So if any 1 could spare the time to explain to me the concept of widgets and how to do a “shop menu” i would be very thank full.

In that situation I would just have the map begin play event trigger the openiing of the UI.