learning php - problem already

Hello everyone, Am new to php and have run into a problem while reading my book... can anybody tell me what does this mean: foreach($invoice as $number => $pppno) and also this: while(list($k,$v,) = each($a)) I do understand for loops and while loops but this is a bit confusing...do you haev any links I can read up on these? Thanks in advance, -Karin Cooke.