What is the usage of Ctrl-N, Ctrl-S and F5?

Answer 1

Ctrl + N: New project (or document)

Ctrl + S: Save your work (if it is the first time you save the project it will ask you where it can save the project)

F5: Run your project

Answer 2

Strg+n: new file
Strg+s: save
F5: run

Answer 3

to run a script in IDLE...

this is explained very well under Basic Concepts/Using Editor in this app. Just read.