{debug} shows a value as a collapsible tree in the page, where the template uses it, and the rendering goes on - unlike {dump}, which stops the request.

<?php

  $order = [ 'number' => 1042, 'customer' => 'Ann', 'lines' => [ [ 'sku' => 'A1', 'qty' => 2 ] ] ];

?>

<p>The order as the template sees it:</p>
{debug $order}

• {debug $name} - one value; an array is a tree to unfold, a missing name says so.
• {debug} - every field visible where it stands: the rows of the enclosing levels, innermost first, and the application's variables.
• Only a local request sees it: the command line, or this machine asking itself with nothing forwarded. Anyone else gets nothing, and $padDiagnostics = FALSE switches it off for every web request - the command line still gets it.