[3-6] I typed a form to the read-eval-print loop, but nothing happened. Why?

There's not much to go on here, but a common reason is that you haven't
actually typed a complete form.  You may have typed a doublequote, vertical
bar, "#|" comment beginning, or left parenthesis that you never matched
with another doublequote, vertical bar, "|#", or right parenthesis,
respectively.  Try typing a few right parentheses followed by Return.