you just need to create an adwords account, and during set up, it will ask for your voucher or coupon, and you just write or paste the code, and that's all, finish to set up your campaign, and you can use it. But beware of your credit limit, hope this helps pal!
Create a new Adwords account. Then you have to fund it with $5 or $10, there is a start up fee. Then google search on 'how to enter my adwords code' so you can see screen shots of how to get to the code redemption screen in your new Adwords account. Then choose some keywords, set a daily budget, and watch your target traffic flow to your website.
Create A New Adwords account Then Apply your Promo code After That Just Activate Your Account With Credit Card/Net Banking Account Thats All
I got the voucher when I opened my Adwords account. But I didn't use it. I think it's only for new accounts.