Keep it up, PHP is one of the best languages to learn IMO. Would have been better to do it like this though:

<?php
  $slotone = mt_rand(1,3);
  $slottwo = mt_rand(1,3);
  $slotthree = mt_rand(1,3);
  echo "Your numbers are: $slotone $slottwo $slotthree<br \><br \>";
  if ($slotone == $slottwo and $slottwo == $slotthree) {
      echo "Congratulations! You have won!";
  } 
  else { echo "You have lost - please try again!"; }
?>

mt_rand() is better than rand() and you really only need a single if-statement.