A single quote is actually shorthand for the quote special form

  'foo
  (quote foo)
  '(1 2 3)
  (quote (1 2 3))

It basically does not evaluate its arguments but returns whatever it is. So instead of the value of foo, it the symbol foo. The list example does not evaluate it either, it would normally try to apply the first element as a function, but instead we get the list of numbers.