Expanding on Timothy's answer...
If you're a web developer looking to use wkhtmltopdf as part of your web app, you can simply install it into your /usr/bin/ folder like so:
cd /usr/bin/
curl -C - -O http://wkhtmltopdf.googlecode.com/files/wkhtmltopdf-0.11.0_rc1-static-i386.tar.bz2
tar -xvjf wkhtmltopdf-0.11.0_rc1-static-i386.tar.bz2
mv wkhtmltopdf-i386 wkhtmltopdf
You can now run it anywhere using wkhtmltopdf.
I personally use the Snappy library in PHP. Here is an example of how easy it is to create a PDF:
<?php
// Create new PDF
$pdf = new \Knp\Snappy\Pdf('wkhtmltopdf');
// Set output header
header('Content-Type: application/pdf');
// Generate PDF from HTML
echo $pdf->getOutputFromHtml('<h1>Title</h1><p>Your content goes here.</p>');