Create one php variable from several

You can do it several ways:

// using sprintf
$address[] = sprintf('%s, %s, %s', $name, $address, $post_code);

// using "Traditional" concatenation
$address[] = "$name, $address, $post_code";

// other version of concatenation
$address[] = $name . ", " . $address . ", " . $post_code;

Or if you want them as an array:

// regular array
$address[] = array($name, $address, $post_code);
// $address[n][0] = name
// $address[n][1] = address
// $address[n][2] = post_code

// keyed array
$address[] = array(
  'name' => $name,
  'address' => $address,
  'post_code' => $post_code
);
// $address[n]['name'] = name
// $address[n]['address'] = address
// $address[n]['post_code'] = post_code  

Since noone else mentioned it, compact()

$name = 'Mike';
$address = '123 Main St';
$post_code = '55555';

$full_address = compact('name', 'address', 'post_code');
var_dump($full_address);

/* Output:
array(3) {
  ["name"]=>
  string(4) "Mike"
  ["address"]=>
  string(11) "123 Main St"
  ["post_code"]=>
  string(5) "55555"
}
*/

Are you simply wanting to append several strings to each other?

If so the correct syntax is this:

$name = 'Dave Random';
$address = 'Some place, some other place';
$post_code = 'AB123CD';

$merged = $name.$address.$post_code;

...using . (dot) to concatentate them. You will probably want to insert a line break, comma etc between them:

$merged = $name.', '.$address.', '.$post_code;

Alternatively, you can specify them all in one new string like this:

$merged = "$name, $address, $post_code";

...note the use of doubles quotes instead of single. It would probably do you well to read this.

Alternatively, you can store them as separate values in an array like this:

$myArray = array();
$myArray['name'] = 'Dave Random';
$myArray['address'] = 'Some place, some other place';
$myArray['post_code'] = 'AB123CD';

...or this:

$myArray = array(
  'name' => 'Dave Random',
  'address' => 'Some place, some other place',
  'post_code' => 'AB123CD'
);

...and your can convert that array to a string with implode():

$merged = implode(', ',$myArray);

For a simple array:

$full_address = array($name, $address, $post_code);

For an associative array:

$full_address = array('name'=>$name, 'address'=>$address, 'zip'=>$post_code);

Do you want to concatenate strings? You should use string concatenation operator ".". For example:

$s1 = "foo";
$s2 = "bar";
$s3 = "blabla";
$final_string = $s1 . " " . $s2 . $s3;
echo $final_string; // output: "foo barblabla"

What you are trying to do is called string concatenation and this is done in PHP with the .-Operator

$name = "Foo";
$address = "Barstreet 1";
$post_code = "12345 Foobar";

$full_address = $name . ", " . $address . ", " . $post_code

You're pretty much almost there.

$name = 'Your name';
$address = 'Your address';
$post_code = 'Your post code';

$full_address = "$name, $address, $post_code";
$address[] = $full_address;

if you want to concatenate name adress and postcode you can do:

$address[] = $name.$address.$post_code;
or 
$address[] = "$name $address $post_code";

if what you want is to add each of the field to the adress array you can do this as :

$address = array($name,$address,$post_code);
or 
$address[] = $name;
$address[] = $address;
$address[] = $post_code;

You could take a look at standard object:

$address = new stdClass;
$address->postcode = '02115';
$address->name = "John Connor';

or create an Address class by itself, it will be quite useful in your app.

class Address {

     public function __construct ($name, $address) {...}
     public function getFullAddress() {...} // or other useful functions
}