If you made the box correctly, then skylight and directional light will not work. That’s right ( you might get some lightness from the skylight ).
If you want light in the box, you either need to put windows in it, or put point lights in it. Just like in real life…
You can’t see the box when you’re in the box, because it doesn’t have any UV on the inside. A quick solution is to make the material double sided ( it’s in the material node details ).
PS: With skylight and directional light, it doesn’t matter where you place them. They light the whole scene. But they don’t usually go through walls 