writeln('test!') is a statement. It invokes a method called
writeln and supplies a parameter 'test!' to it.
writeln means ``write line'', it optionally prints something to
the output and ends the current line. If a program has anything for
writeln to output before it ends the current line, the text to
print must be enclosed by parentheses.
In our example, we want to print test! to the output, therefore
it is enclosed by parentheses after writeln. Note that we also
use the single quote ' to enclose test!. This is because
contents enclosed by a pair of single quotes is considered literal.
For now, don't worry about what is literal; just remember to enclose what
you want to appear in the output in single quotes.