You should have gotten an email from Humble Bundle including a personal link where you have to click on. There you can see the download links to all the games from the bundle and also the steam codes for them (not for Voxatron).
Link example: http://www.humblebundle.com/?key=???????
If you can't find the email, check your spam folder or maybe this could help: click
i have never gotten a email witha personal page for download and redeeming of my Voxatron game, i even checkedd the spam folder, did the resend key, never found it and i have emailed the Lexaloffel games to help me with this but have had no resonse...I'm in quite a predicament