Google Adwords is a beast guys...just needs to be tamed.
I've been doing internet marketing for about 2 years now and with the right product the internet marketing guru's make stupid money, it's insane.
For the average joe who's never tried Adwords, it's a never ending maze that will just suck up your cash. To Google's credit, they provide you with all the info you'd ever need and more to get your ads appearing at the top for the cheapest possible price, you just need to know where to look and be prepared to spend the hours looking into it.
If you're not prepared to study up on it though, I'd just let the voucher expire because the chances of you cracking it first time are near enough zero...the effort you'll put in to the ad, the site, the keyword targeting...it'll just swallow up the money if you don't get a solid campaign ready...
And to begin with you'd probably be better off advertising on the content network as opposed to search as it's cheaper, but you need to know how to get your ads showing up in front of the right people.
As I said though, it's a beast that just needs to be tamed, if you're willing to learn how to tame it, it will work for you and not against you!