hit your Ctrl + Space Bar.
Type insta until you see the choice 'Open a clojure instarepl'
Once you have chosen to Open a clojure instarepl, the Instarepl pops up in lighttable
then type (+ 3 4)
We are used to seeing 3 + 4 = 7, which is called infix notation. However, clojure operates with prefix notation, which is (+ 3 4) = 7. This is also known as polish notation. Reverse polish notation is known as postfix notation and would be (3 4 +) = 7.