I've been working on this list for a while, and I want to release it. This is pretty much all the useful PHP commands that you'll need on a common day basis. I've kept this as simple as I can so that beginners can pick this up as a tutorial of sorts. I go from easy to hard and broad to focused commands.
This is meant to be a 'manual' for if you are confused on how to use a command (or something among those lines). However, if you don't know PHP, reading this will get you well on your way.

THIS GUIDE IS NOT DONE, NOR TESTED!
Commands
PHP start/end
This is how you can start/end your PHP script.
<?php ?>
Newer versions of PHP can also use the shorthand version (not recommended for lack of compatibility!):
<? ?>
Echo
Echo is the command that displays things. Basically, whatever is in the echo is treated as HTML
<?php echo 'test. <b>Bold test.</b> <i>italics</i>'; ?>
If you use the short hand PHP starter, you can also echo using this (not recommended for lack of compatibility!):
<?='test. <b>Bold test.</b> <i>italics</i>'?>
Variables
Variables are like a 'mask' for a specific thing. You store variables like this:
<?php $name = 'Bob'; ?>
The correct syntax for a variable is:
$<VARIABLE NAME HERE>
You can do tons of stuff with variables. For example, echo it.
<?php $name = 'Bob'; echo $name; ?>
If you want to add text you add a concatenator (a period).
<?php $name = 'Bob'; echo 'My name is' . $name; ?>
Echoing two variables side by side is the same as a variable and text.
<?php $name= 'Bob'; $lastname = 'Herman'; echo 'My name is' . $name . $lastname; ?>
Math
You'll find that sometimes you'll need to do math in your script. Unlike texts, numbers do not have to be in quotation marks. However, they can be if it makes sense (such as echoing 'I will be back in 2 hours')
Math is simple. You can add ( + ), subtract ( - ), multiply ( * ) and divide ( / ). You use a variable to store the result.
<?php $result = 2 * 2; echo 'I wonder what 2 times 2 is. Oh wait a sec, it\'s: ' . $result; ?>
(The \ is a commenting slash, which negates the ' effect. Without it, the variable would be ended there that the quotation mark, which would of most likely caused an error. A double slash \\ completely negates a line). With division you can also find the remainder.
<?php $remainder1 = 10%2; $remainder2 = 10%3; echo $remainder1 . ', ' . $remainder2; ?>
That echoes:
Quote
0, 1
You can also do increments. These are useful for when you are counting a specific action. For example, you want to know how many times an action has been done. You can store the amount of times the action has happened with a variable, but you can increase it by one using the increment function. This is how you do it:
<?php $action = '11'; if($_GET['buy'] == 'true') $action++; echo $action;
Although you may not understand everything here, what basically happens is that the script checks if buy is true, and if it is, increment the action by one. What ends up echoing is 12 (if buy is true).
If/Else Statements
If/Else statements is something you'll use a lot in php. Here's the format.
if(condition) { do this }
For example:
<?php $number = '11'; if($number == '11') { echo 'The number is 11'; } ?>
You can also add else statements. This says that if none of the conditions set by the if are met, then do this. For example:
<?php $number = '10'; if($x == '11') { echo 'The number is 11'; } else { echo 'The number is not 11'; } ?>
There is also the intermediate of the if/else... the elseif! The elseif checks if none of the conditions set by the if are met, then do this. The elseif, like the if, has conditions.
<?php $x = '10'; if($x == '11') { echo 'The number is 11'; } elseif ($x == '10') { echo 'The number is 10'; } else { echo 'The number is not 11 nor 10'; } ?>
For one line actions, you can do something like this (I'm using the example from before so that you can compare)
<?php $x = '10'; if($x == '11') echo 'The number is 11'; elseif ($x == '10') echo 'The number is 10'; else echo 'The number is not 11 nor 10'; ?>