how to make a variable in php

1<?php
2  $string = 'string';
3  $number = 1;
4?>

1<?php
2    //can also use print instead of echo and would return  but it is
3    //slower so use echo mainly
4    #variable rules
5    /*
6        - Prefix with a dollar sign $
7        - Start with a letter or an underscore only
8        - Only letters, numbers and underscores
9        - Case sensative
10    */
11
12    #DATA TYPES
13    /*
14        Strings
15        Integers 4
16        floats 4.4
17        Booleans True or Flase
18        Arrays
19        Objects
20        Null
21        Resources 
22    */
23    $output = '  Hello there Bob!!';
24    $num1 = 4;
25    $num2 =10;
26    $sum = $num1 + $num2;
27    $string1 = '  Hello';
28    $string2 = 'Bobby!!';
29    $greeting = $string1 .' '. $string2;
30    $greeting2 = "$string1 $string2";
31
32    $string3 = ' They\'re Here';
33
34    #making a constant
35
36    define('GREETING', ' Hello Everyone!!');
37
38    echo $sum;
39    echo $output;
40    echo $greeting;
41    echo $greeting2;
42    echo $string3;
43    echo GREETING;
44?>

1<?php
2$txt = "Hello world!";
3$x = 5;
4$y = 10.5;
5?>

1$name = "Josh"; //$varname = value

1$varName = "Hello, World";