What does ${ } mean in PHP syntax?

${ } (dollar sign curly bracket) is known as Simple syntax.

It provides a way to embed a variable, an array value, or an object property in a string with a minimum of effort.

If a dollar sign ($) is encountered, the parser will greedily take as many tokens as possible to form a valid variable name. Enclose the variable name in curly braces to explicitly specify the end of the name.

<?php
$juice = "apple";

echo "He drank some $juice juice.".PHP_EOL;
// Invalid. "s" is a valid character for a variable name, but the variable is $juice.
echo "He drank some juice made of $juices.";
// Valid. Explicitly specify the end of the variable name by enclosing it in braces:
echo "He drank some juice made of ${juice}s.";
?>

The above example will output:

He drank some apple juice.
He drank some juice made of .
He drank some juice made of apples.

50 in binary is 11 0010, shift right by 4 yields 11 which is equal to 3.

See PHP documentation and Wikipedia.

=> is the separator for associative arrays. In the context of that foreach loop, it assigns the key of the array to $user and the value to $pass.

Example:

$user_list = array(
    'dave' => 'apassword',
    'steve' => 'secr3t'
);

foreach ($user_list as $user => $pass) {
    echo "{$user}'s pass is: {$pass}n";
}
// Prints: 
// "dave's pass is: apassword"
// "steve's pass is: secr3t"

Note that this can be used for numerically indexed arrays too.

Example:

$foo = array('car', 'truck', 'van', 'bike', 'rickshaw');
foreach ($foo as $i => $type) {
    echo "{$i}: {$type}n";
}
// prints:
// 0: car
// 1: truck
// 2: van
// 3: bike
// 4: rickshaw

It's called an Alternative Syntax For Control Structures. You should have an endwhile; somewhere after that. Basically, it allows you to omit braces {} from a while to make it look "prettier"...

As far as your edit, it's called the Ternary Operator (it's the third section). Basically it's an assignment shorthand.

$foo = $first ? $second : $third;

is the same as saying (Just shorter):

if ($first) {
    $foo = $second;
} else {
    $foo = $third;
}

That style of syntax is more commonly used when embedding in HTML, especially for template/display logic. When embedded this way, it's a little easier to read than the curly braces syntax.

<div>
<? if ($condition): ?>
  <ul>
    <? foreach($foo as $bar): ?>
        <li><?= $bar ?></li>
    <? endforeach ?>
  </ul>
<? endif ?>
</div>

Versus:

<div>
<? if ($condition) { ?>
  <ul>
    <? foreach($foo as $bar) { ?>
      <li><?= $bar ?></li>
    <? } ?>
  </ul>
<? } ?>

The verbose end tags make it a little easier to keep track of nested code blocks, although it's still mostly personal preference.