If you have taken the directives skill, it follows similar logic.
For a definitive location, like outside, in this example, we will use pana. It is used with any specified area. Since we are specifically referring to outside here, we use pana.
If it is an indefinite location, we aren't specifying where something is located, we will use kuna.
Mna is used when we are specifying an enclosed location. For example a box, or a room. So in this sentence if we change 'nje' to 'chumbani' we must also change Pana, to mna.
I hope that helps.