Wordpress Anthology

If I have questions regarding any topics covered in The Wordpress Anthology book offered on this site, would this be the proper forum to present them?

As best a place as any. What do you got?

the author is explaining how to incorporate a form element as part of an edit screen to a custom post. The following code is an excerpt. I don’t understand the function of the $post variable. I’m assuming the $custom variable is essentially the PHP equivalent of $_POST. What I don’t understand is how the post ID is referenced.
$custom = get_post_custom($post->ID);
I was also confused about the second subscript in the $custom index until I glanced at the codex. I noticed that the codex doesn’t bother referencing the second subscript.
Can anyone explain to me the function of the $post variable and the post->ID reference in the following code?

function conference_speaker_fields (){
	global $post;
	$custom = get_post_custom($post->ID);
	$conference_speaker_business = $custom["conference_speaker_business"][0];
	$conference_speaker_website_name = $custom["conference_speaker_website_name"][0];
	$conference_speaker_website_url = $custom["conference_speaker_website_url"][0];
	$conference_speaker_location = $custom["conference_speaker_location"][0];
	<label>Employer/Business Name:</label><br />
	<input size="45" name="conference_speaker_business" value="<?php echo $conference_speaker_business; ?>" />
	<label>Website Name:</label><br />
	<input size="45" name="conference_speaker_website_name" value="<?php echo $conference_speaker_website_name; ?>" />
	<label>Website URL:</label><br />
	<input size="45" name="conference_speaker_website_url" value="<?php echo $conference_speaker_website_url; ?>" />
	<label>Location:</label><br />
	<input size="45" name="conference_speaker_location" value="<?php echo $conference_speaker_location; ?>" /></p>

Hopefully this helps.

The $post object (as in “blog post”, not “form fields”) contains various values.
get_post_custom() uses the ID and returns a multi-dimensional array.

So $custom[“conference_speaker_business”] is not a value but an array that may or may not contain more than one value pairs. It looks like in this example, it is only a single value, hence array key “0”.