The job of performing is to take a 2D script and turn it into a 3D performance. The script is like a footpath marked on a map. There is just a line. The question for the performer is why does it go this way? Why that way? Why does it go up and down when it goes up and down? Why does it go left or right? Why does it wiggle?
The answers of course are it goes left to avoid these rocks, it goes right to avoid that house, it goes down to cross that river, it goes up to reach that summit, over here to go through that gate, across to a bridge, over a style etc
What does that actually mean in terms of doing it?
Consider an improvisation: You mime holding a baby. Then you turn and become the baby. Then, as the baby, you look up at your imaginary mother and you cry. Then you say "Mummy!". And then you cry some more.
Now suppose you need to remember that improvisation so now you want to note it. You could write the paragraph above, but most likely, given that it is barely a moment in the play, you will just write: become the child: cry Mummy!
A script might only have: Mummy! What is not there is the performance. The landscape. All that is there is the line of the path.
The performers job is to take the flat line and recreate the path. To do this you need to imagine all the things around it that affect it and make it what it is. To reverse engineer the 3D improvisation described in the paragraph above, from the 2D, one word, script: Mummy!.