The window above is a MISC prompt. Type a line of MISC code and hit Alt-Enter to run it.
MISC uses a prefix notation, that is the operator comes before the operands ("1 + 2" is written as "+ 1 2"). In MISC these are wrapped in square brackets, for example the sum 137+349 is written as [+ 137 349].
Try some simple expressions:
For the moment MISC can look much like LISP but with square brackets. All of the above examples would be valid LISP if written with normal brackets "()".