In
Mathematica's standard notebook interface, you are directly giving input and getting output every time you press
Shift+Enter. Although much more rarely needed than in more primitive languages,
Mathematica also allows you to get input and generate output as side effects in a computation.
Print — print any expression, including graphics, as output
PrintTemporary — print temporarily, cleaning up when a computation is complete
Input,
InputString — put up a dialog to request input of an expression or string
Import,
Export — import and export in hundreds of formats
