Need help with Breakdown of code block

[Tsalagi]

I am currently studying PHP and not just how to cut and paste and hack someones code. I have this block of code I want to understand fully.
It's from a WordPress theme I'm using to help me learn PHP.
What I don't understand is the foreach loop. Here is what it looks like to my brain. I've included my analysis in comments above each line.

//I understand that $categories_list is a user defined function and is assigned the values that the wordpress function get_categories and it's arguments retrieve.
$categories_list = get_categories('hide_empty=0&orderby=name');

//I also understand that $getcat is a user defined function that is assigned as an array that will be populated with what the foreach loop does.
$getcat = array();

//For each value in the $categories_list as(I see the "as" being an assignment similar to =) $category. In effect assigning a variable to a variable that has not yet been defined or a temporary variable. 
foreach($categories_list as $category) {

//Populate the $getcat array with the temporary variable $category using Wordpress parameters cat_id and cat_name. I don't understand the use of the -> symbols in this line and other places use the => symbol. 
	$getcat[$category->cat_ID] = $category->cat_name;
}
//create a variable $category_dropdown and using the WordPress function 
array_unshift populate the drop-down with $getcat values with "Choose a category:" at the top.
$category_dropdown = array_unshift($getcat, "Choose a category:");

I'd greatly appreciate an analysis of my breakdown and explanation of the sybmols -> and =>.

Thank you in advance

[LarsK]

=> assigning a value to a key in an array:

$myarr = array(
  0 => 'x',
  1 => 'y'
); 

-> calling a function or getting a value of an object

class MyClass {
  public $x = 'y';
  public function myfunction() {
    echo 'Hello world.';
  }
}
$MyClass = new MyClass();
echo MyClass->x;
$MyClass->myfunction(); 

[Tsalagi]

Thanks LarsK. Not once in the books I am studying have I had an explanation of those symbols. They just throw them around like noobs are supposed to have prior knowledge of such things.

[Shrapnel_N5]

I understand that $categories_list is a user defined function

wrong
it's a variable, not a function
and it's quite complex variable.
it's an array of objects
and it means that you've choosen quite complex example to learn
so, -> is just object programming syntax, for accessing object property.
note that => is totally different operator, used in foreach loop to retrieve array key along with value

the rest you've got very well

[Tsalagi]

Thanks for the reply Shrapnel N5. Actually that was a typo. I did mean user defined "variable". I'm glad I chose a complex example because I'm very serious about learning the depths of PHP. I'm breaking down each code block in this theme for starters and then will move on to writing my own. I hope that is a good learning plan. If you have any other ideas as far as how to learn PHP I would love to hear.

Thanks again!